ACTIVITY REPORT 2011

Transcript

1 ISSN DOTTORATO DI RICERCA IN FISICA UNIVERSITÀ DI MESSINA ACTIVITY REPORT 2011 C/O DIPARTIMENTO DI FISICA FACOLTA DI SCIENZE UNIVERSITÀ DI MESSINA Lorenzo Torrisi Editore 1

2 Coordinatore del Dottorato di Ricerca in Fisica Prof. Lorenzo Torrisi Editore Lorenzo Torrisi Assistenti Paola Donato Mariapompea Cutroneo Rocco Vilardi 2

3 DOTTORATO DI RICERCA IN FISICA UNIVERSITÀ DI MESSINA ACTIVITY REPORT 2011 ISSN C/O DIPARTIMENTO DI FISICA FACOLTA DI SCIENZE Università di Messina Viale F. Stagno D Alcontres 312, S. Agata, Messina Lorenzo Torrisi Editore 3

4 INDICE GENERALE Programma 2 a Giornata di Studio del Dottorato di Ricerca in Fisica dell Università di Messina 6 2a Giornata di studio del Dottorato di Ricerca in Fisica dell Università di Messina, 8 Nov L. Torrisi 9 Valutazione nazionale della Qualità della Ricerca (VQR) M. C. Aversa 13 Dottorato di Ricerca e calcolo Scientifico D. Magaudda 15 On the wavelength shift between near-field peak intensities and far-field peak cross sections in plasmonic nanostructures A. Cacciola 21 Mass quadrupole spectrometry applied to laser-produced plasmas and microwave ignited plasmas F. Di Bartolo, L. Torrisi, S. Gammino, F. Caridi, D. Mascali, G. Castro, L. Celona, R. Miracoli, D. Lanaia and R. Di Giugno 25 Fusion reactions in collisions induced by li isotopes on Sn targets M. Fisichella, A. Di Pietro, A. Shotter, P. Figuera, M. Lattuada, C. Marchetta, A. Musumarra, M.G. Pellegriti, C. Ruiz, V. Scuderi, E. Strano, D. Torresi, M. Zadro 31 Particle correlations at intermediate energies and the Farcos project T. Minniti and Farcos/Chimera collaboration 33 Investigation on pseudoscalar meson photoproduction by electromagnetic probe M. Romaniuk, V. De Leo, F. Curciarello, G. Mandaglio, G. Giardina 37 Study of nuclear equations of state: the ASY-EOS experiment at GSI S. Santoro for ASY-EOS collaboration 41 Premio APP per una Tesi di Dottorato P. V. Giaquinta 47 PhD e mondo del lavoro: statistiche sul placement post dottorato P. Donato 49 An overview of research activities in the physics PhD course F. Caridi, L. Torrisi 55 Enhanced optical fields for aggregation of metal nanoantennas and label free highly sensitive detection of biomolecules B. Fazio, C. D Andrea, V. Villari, N. Micali, O. Maragò, G. Calogero and P.G. Gucciardi 61 4

5 Missing resonances at the BGO-OD experiment F. Curciarello, V. De Leo, G. Mandaglio, M. Romaniuk, G. Giardina 65 Resonant laser absorption and self-focusing effects producing proton driven acceleration from hydrogenated structures M. Cutroneo and L. Torrisi 71 Baryon spectroscopy by vector meson photo-production at BGO-OD experiment V. De Leo, F. Curciarello, G. Mandaglio, M. Romaniuk, G. Giardina 77 Diode lasers for optical trapping applications R. Sayed, G. Volpe, M. G. Donato, P. G. Gucciardi and O. M. Maragò 81 Interference with coupled microcavities R. Stassi, O. Di Stefano, S. Savasta 85 Spectral dependence of the amplification factor in surface enhanced Raman scattering C. D Andrea, B. Fazio, A. Irrera, P. Artoni, O.M. Maragò, G. Calogero and P.G. Gucciardi 89 Photoluminescence of a Quantum Emitter in the Center of a Dimer Nanoantenna: Transition from the Purcell effect to Nanopolaritons N. Fina, A. Ridolfo, O. Di Stefano, O. M. Maragò,S. Savasta 93 Lateral Diffusion of DPPC and octanol in a Lipid Bilayer Measured by PFGE NMR Spectroscopy S. Rifici 97 Chemical equilibration of the quark gluon plasma F. Scardina, M. Colonna, V. Greco, M. Di Toro 101 A study about dynamic models on phospholipids A. Trimarchi 105 Ultrafast optical control of light-matter interaction and of wave-particle duality R. Vilardi, S. Savasta 109 Seminari (invited) del Dottorato di Ricerca in Fisica, Effettuati nel Organizzazione del Dottorato di Ricerca in Fisica dell Università di Messina, Ciclo (XXVI) 127 Pubblicazioni 2011 degli studenti del Dottorato di Ricerca in Fisica dell Università di Messina 137 Foto 2 a Giornata di Studio del Dottorato di Ricerca in Fisica dell Università di Messina 145 Indice Autori 155 5

6 2 a Giornata di Studio del Dottorato di Ricerca in Fisica dell Università di Messina 8 Novembre 2011 Biblioteca Centralizzata V.le F. Stagno D alcontres 31, S. Agata, Messina 6

7 Comitato Organizzatore Prof. L. Torrisi Dr.ssa P. Donato Dr.ssa M. Cutroneo Dr. R. Vilardi Comitato Scientifico Prof. G. Carini Prof. P. Giaquinta Prof. G. Giardina Prof. G. Maisano Prof. D. Majolino Prof. L. Torrisi Giornata Organizzata dal Collegio Docente del Dottorato di Ricerca in Fisica e sponsorizzata dall Università di Messina Sito della Giornata di Studio: Biblioteca Centralizzata della Facoltà di Scienze dell Università di Messina, Viale F. Stagno D alcontres 31, S.- Agata, Messina 7

8 9.15 Relazioni di Apertura Saluti del Preside della Facoltà di Scienze MM.FF.NN. Prof. G. Maisano, Direttore del Dipartimento di Fisica Prof. L. Torrisi, Coordinatore del Dottorato di Ricerca in Fisica Prof. D. Majolino, Coordinatore dei CdL in Fisica e Fisica Magistrale Prof. F. Neri, Direttore Dip.to di Fisica della Materia ed Ingegneria Elettronica Prof.ssa M. C. Aversa, Delegata alla Ricerca Scientifica e Tecnologica dell Università Dr.ssa D. Magaudda Responsabile dell Area Sistema Informativo per l Analisi dei Dati e Calcolo Scientifico Dottorato Ciclo XXV Presiede: Prof. G. Carini A. Cacciola (On the wavelength shift between near-field peak intensities and far-field peak cross-sections in plasmonic nanostructures) F. Di Bartolo (Mass Quadrupole Spectrometry applied To Laser-Produced Plasmas and Microwave Ignited Plasmas) M. Fisichella (Fusion reactions and neutron transfer in collisions induced by Li isotopes on Sn targets) T. Minniti (Particle correlations to intermediate energies and the Farcos Project) M. Romaniuk (Investigation on pseudoscalar meson photoproduction by electromagnetic probe) S. Santoro (Study of nuclear equations of state: the ASY-EOS experiment at GSI) Interventi degli Enti di Ricerca Presiede: Prof. G. Giardina Dr. G. Cuttone, Direttore dei LNS, Catania Dr. C. Vasi, Direttore IPCF-CNR, Messina Dr. A. Pagano, Direttore Sez. INFN, Catania Prof. S. Albergo, Direttore del CSFNSM Presiede: Prof. P. Giaquinta Premiazione Tesi di Dottorato di Ricerca in Fisica, Patrocinata dall Accademia Peloritana dei Pericolanti Dr. A. Ridolfo (Quantum Optical Properties of strongly Coupled Systems) Presiede Prof.: G. Mondio Dr.ssa P. Donato, Manager Didattico PhD (PhD e mondo del lavoro: statistiche sul placement post-dottorato) Dr. F. Caridi, Facoltà di Scienze ME (An overview of research activities in the physics PhD course) Dr.ssa B. Fazio, IPCF-CNR (Enhanced optical fields for aggregation of metal nanoantennas and label free highly sensitive detection of biomolecules ) Ciclo XXVI- Presentazione posters Presiede Prof. L. Torrisi F. Curciarello (Missing resonances at the BGO- OD experiment) M. Cutroneo (Resonant laser absorption and selffocusing effects producing proton driven acceleration from hydrogenated structures) V. De Leo (Baryon spectroscopy by vector meson photoproduction at BGO-OD experiment) R. Sayed (Diode lasers for optical trapping applications) R. Stassi (Interference with coupled microcavities: optical analog of spin 2 rotations) Ciclo XXIV- Presentazione posters Presiede Prof. D. Majolino C. D Andrea (Spectral dependence of the amplification factor in surface enhanced Raman spectroscopy) N. Fina (Photoluminescence of a quantum emitter in the center of a dimer nanoantenna: transition from the Purcell effect to nanopolaritons) S. Rifici (Structural changes of lipid bilayers by the addiction of short-chain alcohols) F. Scardina (Chemical equilibration of the quark gluon plasma) A. Trimarchi (A study about dynamic models on phospholipids) R. Vilardi (Ultrafast optical control of lightmatter interaction and of light wave-particle duality) Interventi di chiusura da parte del Collegio Docente Conlusione dei Lavori 8

9 2 a GIORNATA DI STUDIO DEL DOTTORATO DI RICERCA IN FISICA DELL UNIVERSITÀ DI MESSINA MESSINA, 8 NOVEMBRE 2011 Lorenzo Torrisi Coordinatore del Dottorato di Ricerca in Fisica Dip.to di Fisica, Università di Messina V.le F. Stagno D Alcontres 31, S. Agata, Messina La seconda giornata di studio del Dottorato di Ricerca in Fisica dell Università di Messina trova in questa seconda manifestazione un altro particolare momento di riflessione scientifica di notevole rilevanza, di riunione collegiale accademica, meeting di discussione su aspetti di Fisica, consuntivi e Prof. L. Torrisi proponimenti, che coinvolge i Dottorandi della Scuola, il Collegio Docente, gli Organi competenti della Nostra Facoltà e dell Università nonché delle istituzioni scientifiche che collaborano col Dottorato stesso, come l Istituto Nazionale di Fisica Nucleare e il Consiglio Nazionale delle Ricerche. Il Collegio Docente, la comunità dei fisici, quella dei colleghi di altre aree scientifiche e tutti i nostri collaboratori potranno cogliere l occasione di questa giornata per informarsi sullo stato dei lavori del Dottorato di Ricerca in Fisica, orgoglio della Nostra Università. Mediante questo appuntamento sarà possibile conoscere le tematiche delle ricerche in Fisica che si stanno attualmente sviluppando presso il Nostro Ateneo, i progetti che coinvolgono collaborazioni con altre sedi universitarie, centri di ricerca e laboratori esteri, le attività svolte nei laboratori di Messina e in altre sedi collegate. Tali laboratori vedono l avvicendarsi continuamente dei nostri dottorandi in ricerche di ampio respiro internazionale e spesso diventano loro sede di lavoro post-doc. I risultati più innovativi che con essi vengono ottenuti sono stati, e continuano ad esserlo, oggetto di pubblicazioni su riviste ISI con ricadute non solo nel mondo della ricerca e della didattica ma anche in quello sociale. Molte ricerche svolte in seno al dottorato sono infatti pubblicate su riviste ad alto fattore di impatto, molte collaborazioni vengono effettuate con gruppi di ricercatori dei migliori laboratori europei ed extraeuropei, molti risultati trovano applicazione in campo sanitario e ambientale e molti nostri dottori di ricerca trovano occasione di lavoro in questi centri di eccellenza. Partecipare a questa giornata ci permetterà di conoscere meglio le attività di ricerca di gruppi a noi vicini, di una nuova generazione di giovani fisici, e ci potrà permettere di instaurare un discorso scientifico creativo e costruttivo con loro, un occasione che almeno una volta all anno ha motivo di esistere. Logo Università di Messina Nel mio ruolo, colgo l occasione per ricordarvi che il Dottorato di Ricerca rappresenta il massimo titolo per la preparazione scientifica che l Università può conferire ai propri studenti. Oltre la laurea breve, la laurea magistrale, le Scuole di Specializzazione ed i Masters, il Dottorato offre possibilità di apprendimento uniche. Esso si basa non solo sulle lezioni di un Collegio Docente altamente qualificato ed appropriato ma anche su una periodica serie di seminari specialistici tenuti in un contesto Nazionale ed Internazionale che investono i vari Curriculum del Dottorato. Attualmente 31 docenti fanno parte del collegio, 17 sono i dottorandi, 4 i curricula di studio e ogni mese due esperti sono invitati a tenere seminari specialistici di interesse curriculare. I campi di rilievo sono quelli della Struttura della Materia, della Fisica della Materia Soffice e dei Sistemi Complessi, della Fisica Nucleare e della Fisica Applicata all Ambiente, ai Beni Culturali e al Settore Bio-Medico. E in questi ampi settori che il nostro 9

10 dottorando viene portato a svolgere attività di ricerca, usufruendo di una serie di Laboratori altamente adeguati nei quali ha l opportunità di operare dando un proprio contributo. I laboratori dell Accademia delle Scienze della Repubblica Ceca di Praga, l Istituto di Fisica dei Plasmi e di Microfusione Laser di Varsavia, i laboratori GSI di Darmstadt, i laboratori Nazionali dell INFN, l Istituto di Ricerca Nucleare Ucraino INR, l Istituto di Fisica Nucleare Skobeltsyn di Mosca e quello JINR di Dubna, sono solo alcuni dei vari laboratori di eccellenza con i quali il Nostro dottorato può svolgere una continua attività di ricerca e avvalersi di una collaborazione con scambio di studenti e docenti. Collaborazioni rese solide attraverso accordi e protocolli ufficiali che sono stati voluti da alcuni componenti del Nostro Collegio Docente. A loro va un plauso per queste collaborazioni che non nascono dal nulla ma da un intenso, attivo e continuo lavoro, spesso sottovalutato, grazie al quale il nostro Dottorato può emergere e avere un respiro a livello internazionale e l Università di Messina essere menzionata nel mondo. grande mosaico costituisce un piccolo pezzo che si aggiunge a tanti altri che sono venuti e che verranno e che permettono di ampliare le conoscenze umane. Abituarsi a trasferire le proprie conoscenze, ad intercalarle in problematiche più generali, a completarle con altre al fine di poter estrapolare leggi e teorie, è una attività che il dottorando andrà sempre più approfondendo sia durante il dottorato di ricerca che dopo, con l esperienza post-doc. La ricerca mette in moto energie e stimoli di tale vitalità che il meccanismo economico ne trae vantaggio, come una macchina ben alimentata. L innovazione frutto della ricerca ha dunque una ricaduta pratica e concreta anche sulla ricchezza delle nazioni. Ma proprio su questo punto, si impone qualche altra mia considerazione che purtroppo ricalca quanto già detto l anno scorso. La ricerca scientifica Laboratorio di fisica dei Plasmi Laser, Dip.to Fisica, Messina I dottorandi hanno la possibilità di essere inseriti in progetti di ricerca di front-end, di partecipare a lavori scientifici di prestigio e di redigere delle tesi inedite, originali e utili. Per questo sono guidati durante il loro percorso verso corsi e scuole di formazione internazionali che permettono loro di ottenere una più mirata specializzazione sulla tematica di loro maggiore interesse. Ma il loro lavoro ha bisogno di essere maggiormente conosciuto e divulgato. Ciò avviene non solo attraverso le pubblicazioni di lavori scientifici ma anche mediante altri canali, come questa giornata di studio nella quale gli è consentito, di esprimersi e dialogare per avere i giusti input e suggerimenti e un maggiore sostegno durante la sua formazione, necessari all ottenimento di maggiori riconoscimenti e consensi scientifici. Ricordo ai dottorandi che ogni loro risultato, seppur minimo, è prezioso e come in un Ancora oggi in Italia la ricerca scientifica è, come è noto, poco finanziata e i ricercatori sono mortificati dai finanziamenti quasi inesistenti. Inoltre la crisi italiana ed europea nel campo dell occupazione giovanile rende difficile l utilizzo appieno delle capacità che il dottorando ha appreso e spesso egli trova grosse difficoltà di inserimento nel mondo della ricerca e del lavoro post-doc. Sempre più spesso i nostri dottorandi debbono purtroppo trasferirsi all estero regalando ad altre realtà le esperienze acquisite. In questo contesto la giornata di studio attuale vuole rappresentare una denuncia alla nostra società ed ai nostri politici cercando di sensibilizzarli maggiormente verso l importanza della ricerca scientifica in uno stato funzionale. Tuttavia qualcosa si sta muovendo, visto che recentemente il Ministro dell Istruzione, dell Università e della Ricerca ha emanato un regolamento recante i nuovi criteri generali per la disciplina del dottorato di ricerca. Una meritata attenzione che ci fa sperare in un futuro migliore, come verrà tra poco approfondito dalla delegata alla Ricerca Scientifica e Tecnologica dell Università di Messina, Professoressa Maria Chiara Aversa e dalla Responsabile dell Area Sistema Informativo per 10

11 l Analisi dei Dati e Calcolo Scientifico, Dottoressa Dora Magaudda. Inoltre tante iniziative sono in corso per agevolare il finanziamento da parte della comunità europea di specifici progetti di ricerca per i giovani post-doc. Quest anno il Dottorato di Ricerca in Fisica ha ricevuto solo due borse universitarie, una terza l abbiamo ottenuta grazie ai fondi INFN, purtroppo non possiamo avere di più, neppure per studenti stranieri non europei. E un peccato che il nostro dottorato di ricerca, debba subire un decremento di elementi, nonostante il numero crescente di aspiranti studenti sia della sede che da fuori sede. Doctor of Phylosophy Ma noi non ci fermeremo per queste difficoltà perché crediamo profondamente nella formazione e nella Ricerca che in Italia può realizzarsi al meglio anche con le avversità che si spera essere solo momentanee. E per questo ideale oggi siamo qui e presenteremo le nostre attività che reputiamo essere alla base della nostra esperienza di fisici. E grazie a questi ideali che il nostro Dottorato può permettere le sue formative e molteplici attività e mira a promuovere e premiare i giovani con le migliori redazioni di Tesi e di risultati conseguiti, come oggi sarà evidenziato. 1 Report del Dottorato di Ricerca in Fisica, 2010 Vi ricordo che, secondo quanto approvato dall ultima riunione del Collegio docente, che i dottorandi del secondo anno dovranno presentare un intervento sul loro lavoro di tesi mentre i dottorandi del primo e terzo anno un poster e un sintetico sunto. I lavori scientifici che i dottorandi esporranno in questo incontro, sia come contributo orale che come poster, nonché i vari interventi che gli invitati presenteranno, saranno raccolti nel secondo Report del Dottorato di Ricerca in Fisica dell Università di Messina, che sarà pubblicato a breve e che rappresenterà un altro documento duraturo nel tempo, una vera e propria pubblicazione per il dottorando, e una pubblicazione annuale del Dottorato, depositata presso la nostra biblioteca, con numero ISSN già assegnato. RingraziandoVi per l attenzione dedicatami, auguro a tutti voi, colleghi, dottorandi e partecipanti, un buon lavoro. Il Coordinatore del Dottorato di Ricerca Prof. Lorenzo Torrisi 11

12 12

13 VALUTAZIONE NAZIONALE DELLA QUALITÀ DELLA RICERCA (VQR) Maria Chiara Aversa Delegata del Rettore dell Università di Messina per la ricerca in area scientifico-tecnologica Il 7 novembre 2011 è stato pubblicato il bando ufficiale di partecipazione alla Valutazione della Qualità della Ricerca (VQR ) ( L inizio dell esercizio di valutazione nazionale era atteso da tempo, ma probabilmente esso è stato rinviato più volte come conseguenza del passaggio dal Comitato Nazionale per la Valutazione del Sistema Universitario (CNVSU) all Agenzia Nazionale di Valutazione del sistema Universitario e della Ricerca (ANVUR). All epoca della pubblicazione del DM n. 8 del 19 marzo 2010 avente per oggetto Linee guida VQR ( il progetto di valutazione nazionale era limitato a cinque anni e l acronimo VQR corrispondeva appunto a Valutazione Quinquennale della Ricerca. A causa del notevole postergarsi della data d inizio, è stato deciso di includere altri due anni, e si è giunti così al significato attuale dell acronimo. Figura 1 A metà del 2011 si è insediato il consiglio direttivo dell ANVUR (figura 1) costituito da 7 componenti, tutti di estrazione universitaria, presieduto da Stefano Fantoni, professore ordinario di FIS/04 (Fisica nucleare e subnucleare) della SISSA di Trieste, cui si affiancano professori appartenenti alle aree 06 (Scienze mediche), 07 (Scienze agrarie e veterinarie), 09 (Ingegneria industriale e dell informazione), 13 (Scienze economiche e statistiche) e 14 (Scienze politiche e sociali). La figura 1 è congegnata in maniera da mettere in evidenza la distribuzione geografica delle strutture universitarie da cui provengono i 7 componenti del consiglio direttivo, e la distribuzione di genere (cerchi azzurri/rosa): sono solo 2 le donne nel consiglio direttivo, uniche 2 rappresentanti della macroarea umanistica, Fiorella Kostoris Padoa Schioppa e Luisa Ribolzi, entrambe in pensione, la prima dall Università di Roma La Sapienza e la seconda dall Università di Genova. Si tratta di dati che dovrebbero suscitare qualche riflessione. La VQR è coordinata da Sergio Benedetto (figura 1), professore ordinario di ING- INF/03 (Telecomunicazioni) presso il Politecnico di Torino. Il bando di partecipazione alla VQR del 7 novembre 2011 ha lievemente modificato il contenuto dell art. 5 del DM n. 8 del 19 marzo 2010 avente per oggetto Linee guida VQR : in particolare (a) gli articoli scientifici da proporre per la valutazione potranno essere stati pubblicati anche su riviste prive di ISSN e (b) potranno essere proposte anche le traduzioni. Visto che già dal 2010 l Ateneo di Messina prende in considerazione per le proprie valutazioni interne soltanto i prodotti citati dall art. 5 di cui sopra, bisognerà proporre al Senato accademico un eventuale delibera di adeguamento. L ANVUR ha inoltre pubblicato la lista dei presidenti dei Gruppi di Esperti della Valutazione (GEV) (figura 2), uno per ciascuna delle 14 aree CUN. Entro la fine di novembre verrà approvata e pubblicata la composizione dei 14 GEV insieme con i criteri sottostanti alla selezione degli esperti. In analogia alla 1, anche la figura 2 è congegnata in maniera da mettere in evidenza la distribuzione geografica delle strutture di ricerca da cui provengono i 14 presidenti dei GEV, e la distribuzione di genere: ancora una volta soltanto 2 donne, Clara Nervi, professore straordinario presso 13

14 l Università di Roma La Sapienza per l area 05 (Scienze biologiche) e Maria Teresa Giaveri per l area 10 (Scienze dell'antichità, filologico-letterarie e storico-artistiche), attualmente professore ordinario presso l Università di Torino e che ha insegnato Lingua e letteratura francese presso l Università di Messina nel periodo E necessario evidenziare le scadenze temporali che l Università dovrà rispettare nel prendere parte all esercizio della valutazione nazionale della ricerca: a) certificazione elenchi CINECA/MIUR soggetti valutabili (30 dicembre 2011); b) verifica elenchi doc, postdoc, assegnisti, specializzandi area medica (06) (31 marzo 2012); c) trasmissione informazioni mobilità nel settennio (31 marzo 2012); d) trasmissione prodotti di ricerca (30 aprile 2012); e) rapporto di autovalutazione (NV/Rettore) (31 maggio 2012); f) trasmissione brevetti, spin-off, finanziamenti, ecc + elenco nuovi Dipartimenti con afferenti (31 maggio 2012). Il rapporto finale dell ANVUR dovrebbe essere disponibile entro il 30 giugno Tra le innovazioni più significative e gli aspetti più rilevanti del bando VQR del 7 novembre 2011 rispetto ai documenti precedentemente a disposizione, si segnala: a) è stato eliminato il coefficiente di proprietà per i prodotti presentati da più di una struttura; b) è stato eliminato l indicatore di proprietà dei prodotti eccellenti; c) è stato eliminato il vincolo per le strutture di rispettare l ordine di priorità dei prodotti indicato dagli autori; d) globalmente su tutte le aree, almeno la metà più uno dei prodotti saranno sottoposti a peer review; e) la precedente valutazione VTR si è basata su circa prodotti, mentre l attuale VQR è dimensionata intorno a prodotti. Appare opportuno concludere questo contributo citando testualmente la frase di chiusura del messaggio di accompagnamento ( del bando VQR del 7 novembre 2011 a firma di Sergio Benedetto (figura 1): Vi rinnovo l augurio di buon lavoro, nella certezza che insieme affronteremo e risolveremo i molti problemi che si presenteranno strada facendo. Effettivamente solleva qualche perplessità questa mal celata mancanza di sicurezza nella effettività delle procedure, ma, ancora una volta,.. l Università italiana ce la farà! Figura 2 14

15 DOTTORATO DI RICERCA E IL CALCOLO SCIENTIFICO Dora Magaudda Sistemi Informativi per l Analisi dei dati d Ateneo e Calcolo Scientifico CECUM Università di Messina Il Dottorato di Ricerca è stato istituito in Italia solo nel 1980 (legge 21 febbraio 1980, n. 28, D.P.R. 11 luglio 1980, n. 382), e rappresenta il più alto grado d istruzione ottenibile nel sistema universitario italiano e conferisce la qualifica di Dottore di Ricerca, è il più alto titolo accademico conferibile nell ordinamento della Repubblica Italiana. Nel corso degli anni, l andamento di tali corsi è stato attentamente valutato non solo dal MiUR ma anche da tutti i sistemi ufficiali di valutazione, compresi la CRUI, il CNVSU e i Nuclei. La CRUI definisce il Dottorato come il terzo livello di formazione universitaria ed è il grado più alto di specializzazione offerto dalle Università sia per le carriere accademiche e di ricerca sia per quelle nel mondo produttivo, in particolare di quello attento all innovazione. È pertanto necessario che il valore del dottorato sia alto e, come tale, riconosciuto internazionalmente. La formazione dottorale non può che essere fatta con e per la ricerca e quindi richiede, per il suo espletamento, una documentata attività di ricerca ad alto livello. Il dottore di ricerca deve diventare il prodotto finale e più specializzato che l università dà alla società per una classe dirigente preparata e consapevole. Il nuovo statuto dell Università di Messina ha posto l istituzione dei Dottorati di Ricerca tra i suoi interessi primari: tra gli organi di Governo è stato inserito, tra gli altri, il Collegio dei Coordinatori delle Scuole di Dottorato. Problematiche rilevate sui dottorati di ricerca e indicazioni ministeriali per le loro soluzioni Già nel , il CNVSU auspicava che fossero incoraggiati alcuni comportamenti volti a salvaguardare le finalità del Dottorato di Ricerca, chiedendo ai Nuclei di Valutazione di monitorarle: a) contenimento dell eccessiva frammentazione, ciò potrebbe infatti comportare: a. una docenza e un programma formativo inadeguati b. uno scarso numero d iscritti e di borse. Così come con la 509 si è avuta una larga proliferazione di Corsi di Studio non facilmente spendibili nel mondo del lavoro, anche per i Dottorati di Ricerca ci si è trovati di fronte ad una situazione simile. Per tali ragioni, il CNVSU è sempre stato favorevole a iniziative di accorpamento, che portino alla costituzione di Scuole di Dottorato. Questo è un compito abbastanza semplice per i Nuclei, laddove si riscontrino dottorati che nel loro piano di studi abbiano aree disciplinari sovrapponibili; ma quando questa sovrapposizione non esiste o richiederebbe conoscenze approfondite, diviene necessaria una peer review che non è sempre effettuabile da parte dei Nuclei stessi. b) concentrazione in un unica sede delle attività didattiche dei dottorati consorziati. Questa valutazione è abbastanza semplice per i Nuclei c) opportuna ricerca di fonti esterne di finanziamento, onde consentire la creazione di figure professionali appropriate a creare sbocchi occupazionali, laddove, soprattutto, le fonti di finanziamento esterne siano erogate da Aziende interessate alla ricerca. Altrimenti, c è il rischio che il titolo possa essere considerato come una semplice estensione del percorso formativo della laurea. Questa valutazione è abbastanza semplice per i Nuclei d) creazione di una spinta all internazionalizzazione, con la creazione di percorsi preferenziali per l accesso di studenti stranieri o di altre Università, tramite l istituzione di borse apposite e incentivando la collaborazione con Atenei stranieri. Anche questa valutazione è abbastanza semplice per i Nuclei, ma solo in fase di Consuntivo, in quanto, nella fase di Attivazione o di Rinnovo di un Dottorato di Ricerca, i collegamenti con altre Università ed Enti, italiani o stranieri, non possono ancora essere formalizzati, dato che la valutazione del Nucleo avviene prima della decisione della Governance dell Ateneo sui dottorati da attivare e sul numero di borse d assegnare ad ognuno. 15

16 Negli anni passati, a partire dall esercizio 2002, si è avuta una ripartizione del 20% di finanziamento alle Università per i Dottorati di Ricerca che rispondessero ad alcuni requisiti precisi, che sono stati recepiti anche dal Nucleo di Valutazione dell Università di Messina e saranno discussi in seguito. Essendo stata concessa grande autonomia alle università che decidono: L istituzione dei corsi di dottorato Le modalità di accesso e conseguimento del titolo Gli obbiettivi formativi ed il relativo programma di studio La durata Il contributo per l accesso e la frequenza Le modalità di conferimento e l importo delle borse di studio. il problema che si è prospettato è stato della impossibilità di definire in maniera chiara e univoca per tutte le Università i termini di attivazione dei Dottorati. I Nuclei si sono trovati di fronte al problema di standardizzare (almeno a livello di Ateneo) le valutazioni dei Dottorati di Ricerca. ll Nucleo di Messina ha stabilito che, laddove fosse esprimibile con un indicatore un requisito ministeriale, di considerarlo come indispensabile per l assegnazione di un valore, affinché l Ateneo potesse concorrere a questa quota di finanziamento La legge 30 Dicembre 2010, n. 240 Con l introduzione della nuova legge del 30 Dicembre 2010, n. 240, si è arrivati alla proposta di una nuova e più ampia visione dei corsi di Dottorato, rivisitata anche in base alle esperienze pregresse. Anche in questo caso, si pone l accento sulla partecipazione dei Dottorandi ai gruppi e ai progetti di ricerca e si richiede di esaminare la necessità di una valutazione periodica della produzione scientifica dei dottorandi. Questa valutazione si dimostra piuttosto problematica sin da oggi, in quanto tra le varie aree scientifiche-disciplinari, e soprattutto tra le macro-aree umanistiche e scientifiche, si ha una notevole differenziazione nella preparazione alla ricerca dei dottorandi stessi. Un esempio per tutti è quello dei dottorati in aree letterarie, dove il dottorando prepara la sua tesi, che deve essere inedita, in genere tramite una monografia e non tramite più articoli su rivista o altro come avviene nelle aree scientifiche. Questo modus operandi porta alla pubblicazione della tesi solo dopo l esame finale di Dottorato: ne consegue una forte difficoltà per i Nuclei nella valutazione annuale dei consuntivi dei dottorati di ricerca di questo tipo. Un altra differenza fondamentale si può riportare a proposito della numerosità degli autori: in generale, nelle pubblicazioni scientifiche, si hanno collaborazioni tra più settori scientifici disciplinari e/o più macro-aree, ne consegue che il numero di autori può essere molto superiore a quello di coloro che hanno produzioni eminentemente umanistiche (in generale un solo autore). Il Nucleo di Messina ha recepito le difficoltà espresse dai Coordinatori delle Aree Umanistiche, suddividendo i risultati delle valutazioni nelle due macro-aree distinte; ma nonostante ciò esistono problematiche non risolvibili semplicemente con una standardizzazione del calcolo degli indicatori. Un altro punto importante cui si fa espressa menzione è che non può essere accettabile la consecuzione del titolo di dottore di ricerca oltre i 30 anni, dato che dovrebbe essere possibile entrare nella fase post-doc o lasciare l Università attorno ai anni, evitando un inserimento tardivo nella realtà professionale. Il Nucleo di Messina probabilmente modificherà il calcolo dell indicatore, per quanto lo abbia già fatto in passato differenziando i punteggi dei dottorandi senza borsa, con borsa e con borsa di altra amministrazione. E necessario sottolineare che la legge non prevede risorse sufficienti per la propria applicazione, quindi neanche per il dottorato di ricerca: allo stato attuale il taglio di oltre il 30% verificatosi nell ultimo triennio potrebbe arrivare a raggiungere circa il 50% dei posti messi a concorso. Si presume che i circa dottorandi possano ridursi a meno di : ciò significherebbe una consistente riduzione del sistema dell Alta Formazione. Si ipotizza, dal testo della legge, che si avrà una forte incentivazione dell istituzione dei Dottorati senza borsa (senza, per altro, consentire almeno una notevole riduzione delle tasse di iscrizione) anche se l interpretazione della disciplina sulle borse di studio è controversa, pur essendo rimodulato l importo minimo della borsa stessa, che in Italia, rispetto ad altri paesi europei è molto contenuto. L Art. 7 Interventi di cooperazione interuniversitaria internazionale strutturata prevede che solo vengano destinati a consolidare e incentivare interventi di università italiane, di studenti, laureati e dottorandi provenienti da Paesi extraeuropei 1 Questi dati sono messi a disposizione dall ANDI 16

17 in linea con le politiche ministeriali di cooperazione internazionale. Il numero minimo di borse di dottorato passa da 3 a 6: ma non è chiaro se quest ultimo numero è da intendersi solo per le Scuole di Dottorato o per i corsi di dottorato. In quest ultimo caso, quelli attivabili presso ciascuna Università dovrebbero essere molto meno numerosi, soprattutto nei casi in cui la reperibilità di risorse esterne, fortemente dipendente, com è ovvio, dal bacino geografico su cui insiste la singola Università, è problematico. Il Nucleo, anche in questo caso, può giudicare il numero di borse solo dopo la loro assegnazione, quindi in fase di consuntivo La legge chiede anche una valutazione dell impatto professionale del titolo. Il precedente Nucleo di Valutazione aveva inserito nelle sue valutazioni una tabella in cui si chiedeva ad 1 anno, a due e a tre quale fosse l attività lavorativa intrapresa dal dottorando e se fosse coerente con il percorso di studi. I dati ricevuti in risposta sono piuttosto scarni e quindi non significativi, perché non sempre era possibile contattare i dottorandi stessi Attivazione dei corsi di dottorato e ruolo del nucleo Come si è già detto, i Nuclei di Valutazione hanno dovuto, nel corso degli anni, giudicare i Dottorati di Ricerca in base a determinati requisiti, che la 240 ha reso più stringenti. Il Nucleo di Messina ha concepito una scheda di richiesta rinnovo/nuova attivazione ed una di Consuntivo che contenesse tutte le informazioni necessarie alla valutazione dei Dottorati di Ricerca. In tal modo, avrebbe potuto effettuare le sue valutazioni nella maniera più corretta in base alle indicazioni ministeriali. A tale scopo, ha chiesto alla propria Referente Informatica, capo Area Sistemi Informativi per l Analisi dei dati d Ateneo e Calcolo Scientifico, la creazione di un software apposito. Il risultato è stato considerato molto soddisfacente sia dal Nucleo che dall utenza, per la semplicità d uso e le facilities inserite che lo rendono intuitivo ed efficace. In sintesi il software si compone di sei parti fondamentali: 1. Compilazione della scheda di richiesta rinnovo/nuova attivazione da parte del Coordinatore 2. Compilazione della scheda di consuntivo per ogni ciclo attivo da parte del Coordinatore e dei Dottorandi 3. Attestazione della correttezza delle dichiarazioni informatizzate da parte dell Ufficio Dottorandi che convalida, in base al cartaceo presentato dai Coordinatori, quanto da loro stessi dichiarato 2 4. Attestazione della validità delle dichiarazioni dei dottorandi da parte del Nucleo di Valutazione 3 5. Procedura automatizzata di calcolo dei punteggi degli indicatori 4 Procedura di visualizzazione dei punteggi degli indicatori di tutti i dottorati. La procedura consente la visualizzazione di tutti i dettagli ed è visibile a tutti i Coordinatori. Gli indicatori considerati sono 8 e rispecchiano, dove possibile, le richieste del Ministero in maniera dettagliata, ovvero i criteri concordati con la Governance d Ateneo laddove quelli ministeriali siano nebulosi o non ben descritti. Rispetto ai primi calcoli, sono state apportate modifiche delle quali via via si sentiva il bisogno, dettate sia dalle differenze tra la conduzione dei dottorati di ricerca (per esempio tra le due macro aree Umanistica e Scientifica) sia dalle le diverse necessità di conduzione dei dottorati, dovute a svariati motivi 5 : tali differenziazioni sono state discusse durante alcune riunioni con i Coordinatori di Dottorato. Particolare attenzione è stata posta nella valutazione dei prodotti della ricerca, resa possibile grazie alla presenza del Catalogo di Ateneo informatizzato, che è stato lo strumento principe per poter creare il software necessario. Anche in questo caso, la valutazione di tali prodotti è stata stabilita, una prima volta e successivamente modificata, di concerto con la Governance dell Ateneo. E importante sottolineare come alcune decisioni siano state oggetto di critiche in quanto alcuni Coordinatori trovavano i criteri troppo stretti per le esigenze della loro Area. Ma anche queste perplessità sono state considerate e in parte risolte nell ambito della forte collaborazione tra il Nucleo e la Governance dell Ateneo. 2 Attestati dei professori di altri Atenei presso i quali si sono recati i dottorandi, attestazione dell incremento delle borse per soggiorni all estero, lettere di partecipazione esclusiva di un docente italiano al dottorato, curricula dei docenti stranieri e italiani non di Messina (per i Messinesi esiste il Catalogo di Ateneo che è stato uno strumento indispensabile per il buon funzionamento dell impianto delle schede informatizzate). 3 Si tratta di convalidare o meno le dichiarazioni che talvolta sono inserite per inesperienza, ma che non possono dare adito a calcoli per i punteggi degli indicatori, quali, ad esempio, le ore impiegate nella ricerca o negli incontri con il Coordinatore e/o i tutor per la preparazione della tesi. 4 La procedura è del tutto indipendente dalle altre, per consentire l effettuazione di modifiche nei calcoli nel modo più semplice. 5 Si pensa ai periodi di permanenza all estero che, in generale, danno adito a punteggio solo se sono di almeno tre mesi, mentre per gli scavi archeologici e la permanenza sulle navi scendono a 1 mese. 17

18 Per una totale trasparenza del proprio operato, il Nucleo ha inoltre richiesto che il software, alla chiusura del periodo di richiesta di Rinnovi e o Nuove Attivazioni e delle convalida amministrative 6, permettesse a tutti i Coordinatori la visione dettagliata dei calcoli degli indicatori di tutti i Dottorati. Si può ragionevolmente affermare che quello dell Ateneo di Messina è stato, in Italia, il primo impianto logico e software completo che ha consentito la formalizzazione delle valutazioni sui Dottorati di Ricerca: molte altre Università hanno, infatti, seguito un modello molto simile. Nel Dicembre 2008 la procedura è stata presentata nel convegno tenutosi a Padova cui hanno partecipato tutti i Nuclei di Valutazione. Purtroppo però, nonostante le richieste ricevute, il nostro Ateneo non è stato in grado di fornire tale software ad altre Università. Un ulteriore punto a favore del lavoro svolto, è la dedizione con cui il Prof. Mondello si è dedicato alla valutazione della correttezza delle dichiarazioni nelle schede ed a suggerimenti volti al miglioramento ed alla semplificazione della procedura; per la parte operativa sento il bisogno di ringraziare la serietà e la professionalità del Dott. Marco Todaro e dell Ing. Fabrizio De Gregori, che, con la procedura menzionata, hanno consentito un notevole risparmio economico alla nostra Università. Il software si riferisce a due fasi distinte della valutazione dei dottorati di ricerca: quella della richiesta di Rinnovo/nuova Attivazione e quella di Consuntivo, dove, al di là di alcune informazioni fornite dai Coordinatori, ogni Dottorando indica il percorso formativo svolto e il risultato delle sue ricerche. 6. Esistenza di un piano formativo formalizzato e documentato 7. Produttività Scientifica di Ricerca pro capite dei Dottorandi 8. Contesto Scientifico (Progetti di ricerca) Nella tabella seguente si mostrano le differenze tra la vecchia legislazione, quanto richiesto dalla L.240 e l impianto logico, nelle schede del Nucleo, per il calcolo degli indicatori: Come si è già detto gli indicatori sono 8, ed ognuno di essi serve a quantificare una delle richieste ministeriali, comprese quelle della 240, per la quale basterà modificare soltanto il modulo di calcolo dei punteggi: 1. Numerosità del Collegio Docenti 7 2. Produttività Scientifica del Coordinatore 3. Produttività Scientifica pro capite del Collegio Docenti 4. Accordi di collaborazione per lo svolgimento di esperienze in un contesto di attività lavorative o per lo svolgimento di stage in sedi di ricerca qualificate straniere o italiane 5. Posti di dottorato aggiuntivi rispetto alle borse finanziate dall Ateneo 6 Egregiamente effettuate dall Ufficio Dottorati che non si potrà mai ringraziare abbastanza. 7 Il collegio docenti può essere formato solo dai docenti indicati come tali dal MiUR. 18

19 Requisiti Ministeriali Precedenti Requisiti Ministeriali L. 240 Indicatore corrispondente la presenza nel collegio dei docenti di un congruo numero di professori e ricercatori dell'area scientifica di riferimento del corso. Non meno di 7 docenti per l attivazione Non meno di 10 per il 20% del finanziamento la disponibilità di adeguate risorse finanziarie la disponibilità di specifiche strutture operative e scientifiche per il corso e per l attività di studio e di ricerca dei dottorandi la previsione di un coordinatore responsabile dell organizzazione del corso la previsione di un collegio di docenti e di tutori in numero proporzionato ai dottorandi: non veniva specificato però il significato di congruo la previsione di un collegio di docenti e di tutori con documentata produzione scientifica nell ultimo quinquennio nell area di riferimento del corso la possibilità di collaborazione con soggetti pubblici o privati, italiani o stranieri, che consenta ai dottorandi lo svolgimento di esperienze in un contesto di attività lavorative la previsione di percorsi formativi orientati all'esercizio di attività di ricerca di alta qualificazione presso università, enti pubblici o soggetti privati l attivazione di sistemi di valutazione relativi alla permanenza dei requisiti di cui al presente comma l attivazione di sistemi di valutazione relativi alla rispondenza del corso agli obiettivi formativi di cui all articolo 4 l attivazione di sistemi di valutazione relativi alla rispondenza del corso agli obiettivi formativi in relazione agli sbocchi professionali, al livello di formazione dei dottorandi Collegio docenti formato almeno da 18 8 professori 9 attivi 10 Non sono stabiliti in modo esplicito Non sono stabiliti in modo esplicito Non cambia nulla rispetto alla normativa precedente INDICATORE 1 Collegio docenti formato almeno da 18 professori 8, 9, 10 Collegio Docenti Non cambia nulla rispetto alla normativa precedente Sono auspicati e se ne chiede l incremento, ma non vengono fornite adeguate risorse finanziarie. Sono auspicati e se ne chiede l incremento, ma non vengono fornite adeguate risorse finanziarie. Non sono specificati meglio neanche nella 240 Non sono specificati meglio neanche nella 240 Non sono specificati meglio neanche nella 240 Scheda in cui si trovano le informazioni INDICATORE 1 11 Richiesta Rinnovo /nuova Numerosità del Collegio Docenti Attivazione INDICATORE 8 Contesto Scientifico (Progetti PRIN, FIRB finanziati e/o finanziabili e Progetti della Comunità Europea Finanziati 12 ) Numero massimo di dottorandi compatibili con le strutture organizzative INDICATORE 1 Coordinatore. Non è possibile inserire una scheda senza un Coordinatore Richiesta Rinnovo /nuova Attivazione Richiesta Rinnovo /nuova Attivazione Richiesta Rinnovo /nuova Attivazione Richiesta Rinnovo /nuova Attivazione INDICATORE 2 e 3 Richiesta Rinnovo /nuova Produzioni scientifiche del Coordinatore e del Collegio Docenti 10 Attivazione INDICATORE 4 INDICATORE 5 13 Periodo formativo all estero Accordi di collaborazione / convenzioni per lo svolgimento di esperienze in contesto di attività lavorative Forme di collaborazione per lo svolgimento di esperienze in contesto di attività lavorative non formalizzate 14 INDICATORE 6 Programma formativo, modalità di svolgimento e finalità del corso Obiettivi formativi orientati alla ricerca e tematiche di ricerca Indirizzi e tematiche di ricerca INDICATORE 7 Produttività scientifica pro-capite dei dottorandi Modalità di valutazione periodica della preparazione dei dottorandi al fine della prosecuzione del corso Sbocchi professionali previsti Schede Consuntivo dei singoli Dottorandi Schede Consuntivo dei singoli Dottorandi Schede Consuntivo dei singoli Dottorandi Richiesta Rinnovo /nuova Attivazione Richiesta Rinnovo /nuova Attivazione Valutato SI SI NO SI SI SI SI SI SI NO NO 8 ordinari e associati del/i settore/i concorsuali o SSD oggetto del corso, attivi in ricerca, ovvero, nei settori è opportuno, di esperti di elevata qualificazione di numero non superiore a quello dei docenti) 9 Art.5, comma 1, punto a dello Schema di decreto del MiUR Regolamento recante criteri generali per la disciplina del Dottorato di ricerca del 27/09/ Per attivo si intende un professore che abbia pubblicato almeno tre prodotti della ricerca negli ultimi 3 anni ovvero, se dell aria umanistica, almeno 1 monografia. 11 Il Professore Ordinario attivo vale 1 punto, il professore associato attivo vale 0,7 punti, il ricercatore attiva vale 0,5 punti. Il Professore non attivo non da adito a punteggio. 12 I coordinatori nazionali o locali devono essere dell Università di Messina 13 Posti di Dottorati aggiuntivi rispetto alle borse d Ateneo: borse finanziate dalla comunità europea, PON, PRO, POM, Enti pubblici e/o privati, PRIN, FIRB, FSG, posti attivati con mantenimento dello stipendio dell amministrazione originaria. 14 In generale il soggiorno in Italia dovrà essere di almeno 3 mesi, mentre per quelli all estero in sono valutati in quota parte ai 3/1 mese (v. nota 5) solo se vi sia un incremento della borsa.

20 Calcolo scientifico A proposito della Ricerca Scientifica, e quindi anche in relazione alla produttività scientifica pro-capite dei dottorandi, è importante fare un ulteriore discorso. Quale Responsabile dell Area Sistemi Informativi per l Analisi dei dati d Ateneo e Calcolo Scientifico, gestisco, validamente coadiuvata dall Ing. Sciacca e dal Dott. Lo Re, il Settore di Calcolo Scientifico del CECUM, mettendo a disposizione dei Ricercatori dell Ateneo un insieme di risorse di calcolo piuttosto consistente: il cluster eneadi, costituito da sei server HP Integrity quadriprocessori e da un server HP ProLiant biprocessore per un totale di 26 CPU. Nello stesso rack si trovano i server HP ProLiant che eseguono Windows Server 2003 e consentono all utenza l uso dei programmi MATHLAB e MATEMATICA, utilizzabili direttamente dal portale di calcolo. Il server Xanto (DL360), invece, insieme ai due server Voltumna (SUNBLADE100) e Larsthurms (SUNBLADE2000) sono utilizzati per la gestione del sito e dei software del Settore di Supporto al Nucleo di Valutazione della stessa area. Per quanto riguarda il dimensionamento di queste ultime apparecchiature è necessario dire che esse erano state acquisite per un numero di accessi piuttosto limitato, in quanto, fino al 2007, il software a disposizione del Nucleo di Valutazione era piuttosto limitato. Da quando sono state sviluppate le procedure principali delle richieste di Attivazione / Rinnovi dei Dottorati di Ricerca e di Valutazione della Didattica (arrivati rispettivamente alle versioni 5.0 e 2.7), il bacino di utenza si è allargato a tutti i Coordinatori dei Dottorati di Ricerca, ai Dottorandi per ciò che concerne la prima procedura, ai Referenti di Facoltà, a tutti i Docenti e gli studenti per ciò che riguarda la Valutazione della Didattica, per un totale di oltre utenze potenzialmente concorrenti; Il cluster TriGrid, formato da un insieme di 28 lame IBM LS20 e 21; Nei due sistemi è installato il software LSF (Load Sharing Facility) e librerie per il calcolo parallelo. In generale l uso delle risorse offerte dal Settore di Calcolo Scientifico viene effettuato da parte di un gruppo ormai consolidato di utenti, il cosiddetto gruppo storico, ma ad essi se ne stanno via via aggiungendo altri che hanno iniziato a sfruttarle per le proprie attività di ricerca o per altri progetti 15. In quest ottica le risorse offerte dal Settore di Calcolo Scientifico si sono rivelate molto significative, tenuto conto che sul cluster eneadi, nel solo 2010, sono stati eseguiti con successo ben job correlati al progetto di cui in nota, i quali hanno richiesto un tempo totale di CPU pari a secondi, corrispondenti a 66 giorni di calcoli; il tempo medio di CPU richiesto da questi job è stato dunque di 3.016,3 secondi, e il valore massimo registrato è stato di secondi. Poiché è capitato che l esecuzione contemporanea di più job eccedesse le risorse a disposizione, con la conseguente necessità di mettere in coda uno o più job, si è avuto un tempo totale di attesa in coda pari a ben secondi, con una media di 1.290,6 secondi e un valore massimo di secondi, addirittura superiore al massimo tempo di CPU impiegato dai job del progetto. Quanto appena detto evidenzia come, pur limitatamente ai periodi di svolgimento dei calcoli che riguardano determinate attività di ricerca, le risorse del cluster eneadi che fino a qualche anno fa erano in grado di soddisfare ampiamente le richieste dell utenza possano oggi rivelarsi sottodimensionate rispetto al fabbisogno di quest ultima; a causa di ciò, nata l esigenza di poter disporre di nuove risorse di calcolo, si sta lavorando all allestimento del nuovo cluster IBM precedentemente impiegato nell ambito del progetto TriGrid. Il cluster eneadi è formato da server che vengono sfruttati con regolarità sia dall utenza scientifica che da studenti e dottorandi di ricerca. Nella fornitura di potenza di calcolo all'utenza va menzionato per la sua crescente importanza il cluster IBM (ex TriGrid). Se ne stanno rimodulando le impostazioni (riconfigurandolo) al fine di offrire un'equa distribuzione delle risorse, dato che tale cluster viene già attivamente utilizzato da un gruppo di utenti. L'alta densità di core per unità di rack disponibili, resa possibile dall'adozione di blade IBM dotate ciascuna di due processori Opteron dual core, consente l uso di un elevato numero di core per le elaborazioni, anche di tipo parallelo grazie all'impiego di apposite librerie. I sistemi di calcolo scientifico messi a disposizione del CECUM sono utilizzati anche in seguito ad una visione allargata della ricerca. Infatti molti docenti iniziano i loro studenti all uso di risorse di questo genere nell ambito delle materie di cui sono titolari. Ovviamente oltre agli studenti i due sistemi sono pesantemente utilizzati anche dai borsisti, dai dottorandi di ricerca, laureandi e, eventualmente, sono stati creati account per visiting professors. 15 Dal 2010 il Dipartimento di Ingegneria Civile partecipa ad un progetto di ricerca europeo sullo sviluppo di tecnologie sostenibili innovative per l energia, dal titolo THermoacoustic Technology for Energy Applications (THATEA, il progetto è coordinato dall Energy Research Centre of the Netherlands (ECN) e vede la partecipazione di importanti Università ed Istituzioni di ricerca europee quali l Università di Manchester ed il CNRS. 20

21 ON THE WAVELENGTH SHIFT BETWEEN NEAR-FIELD PEAK INTENSITIES AND FAR-FIELD PEAK CROSS SECTIONS IN PLASMONIC NANOSTRUCTURES Adriano Cacciola Dottorato di Ricerca in Fisica dell Università di Messina Viale F. Stagno D Alcontres, S. Agata-Messina, Italy acacciola@unime.it Abstract The localized plasmons of metallic nanoparticles and nanostructures display a particular behaviour: when they are optically excited, the near-field peak intensities occur at larger wavelengths than the farfield peak intensities. Here we show that the magnitude of this shift depends on the dimensions of these nanostructures and is theoretically predictable through an approach based on the multipole expansion of the electromagnetic fields within the Transition Matrix formalism. The understanding of this phenomenon is particularly important for Surface Enhanced Raman Spectroscopy (SERS). Introduction Metal nanoparticles (MNPs) have been intensively studied within the past decade. The unique properties of MNPs have their applications in a broad range of different fields, including chemistry, physics, biology, materials science, medicine, catalysis and so on [1]. These applications rely heavily on the fact that MNPs support localized surface plasmon resonances (LSPRs), which are excited when incident electromagnetic radiation creates collective coherent oscillations of the particle free electrons [2]. Such plasmon excitations result in a large enhancement of the electromagnetic field around the nanoparticle, yielding both a strong absorption and scattering of light by the nanoparticle at the plasmon resonance frequency [3]. Varying the size and shape of metal particles we can tune the plasmon resonances over a wide range of wavelengths [1,2,3]. Thus, understanding the properties of plasmonic structures of different size and shape is nowadays of primary importance for basic and applied research as well as for modern nano-technology [1]. Although extinction, absorption, and scattering are still the primary optical properties of interest, other spectroscopic techniques, e.g. SERS, are sensitive to the electromagnetic fields at or near the particle surfaces, thus providing important new challenges for theory. A well known phenomenon, that has frequently been pointed out in the literature, is that, upon optical excitation, the maximum near field enhancements occur at lower energies than the maximum of the corresponding far-field quantities [4,5,6,7]. This red shift is known to depend on the size of the particle [8,9], with larger particles displaying a more marked shift. A recent systematic study has provided a phenomenological comparison of the relationship between the near- and far-field spectra of plasmonic particles [10], but the physical explanation of this apparently universal behaviour of metal particles is still controversial. Messinger et al. [4] explain this behaviour in terms of the radial components of the electric field which can exist only in the near-field zone of the sphere. Recently Zuloaga and Nordlander [11] have explained the physical origin of this red shift through a mechanical analogy as a general consequence of the behaviour of damped harmonic oscillators. In this paper we analyze the red shift effect through an analytical and numerical approach based on the multipole expansion of the electromagnetic fields within the Transition Matrix (T-Matrix) formalism [12]. We will investigate the dependence of this red shift upon the nanoparticle size and shape. To this aim we start our investigation with a gold sphere and successively we extend the description to the case of gold dimers. Theory We study the optical behaviour of metal nanoparticles, both isolated or clustered, through the multipole expansions of the electromagnetic fields within the T-Matrix method. This is a general approach that applies to particles of any shape and refractive index and for any choice of the radiation wavelength [12]. It has been successfully applied to several research fields, e.g. for the investigation of interstellar dust optical properties [13,14,15], in bioastronomy [16,17], and in optical trapping [18,19,20,21]. Expanding the incident field in a series of vector spherical harmonics with known amplitudes W p I lm, the scattered field can be expanded on the same basis with amplitudes A p' lm ' '. The relation between the amplitudes of scattered and incident field is given by 21

22 A S W p' p' p p l ' m' l ' m' lm I lm plm (1) direction for a 100 nm gold sphere. The spectra have been normalized to their maximum values. where S is the T-Matrix of the particle[9]. The pp ' l ' m' lm elements of the T-Matrix are calculated in a given frame of reference through the inversion of the matrix of the linear system obtained by imposing the boundary conditions to the fields across each spherical surface [12]. The number of subunits are limited only by the memory demand of the computing facilities. The calculation of the T-Matrix for a N-sphere aggregate, requires the inversion of a matrix of order d = 2N l M (l M +2), where l M is the l-value at which the multipole expansion of the electromagnetic fields is truncated [12]. The choice of the value l M is carefully checked by convergence tests ensuring the numerical stability of the results. The procedure devised for the extension of the T- Matrix formalism to the study of the optical behaviour of an aggregate of N, not necessarily equal, spheres whose mutual distances are so small that the interaction effects cannot be neglected can be found in [12]. In such case the T-Matrix approach allows to take proper account of the multiple scattering processes among the spheres composing the aggregate. In Fig. 1 we compare the normalized scattering cross section with the normalized Near Field scattered Intensities (NFI) for three different points located at a distance d NF from the sphere surface given by 1/10 of the radius. This choice for d NF has been used in all the results that we will show. All the spectra have been normalized to their maximum values. As is evident from the figure, the NFI is red shifted from the far-field spectrum. This effect appears more clearly in the backward direction and at 90 respect to the incident direction. In the forward direction only the quadrupole peak appears and the red shift is much smaller. Along the polarization direction the quadrupole peak almost disappears and all the energy radiated by the particle is mainly due to the dipole contribution. Results We start our investigation with a spherical gold nanoparticle with a radius of 100 nm. The direction of the incident field is along the z-axis and the polarization is along the x-axis. This configuration has been used in all our computations. Figure 2: Scattering cross sections (solid lines) and NFI (dotted lines) for a 30 nm gold sphere (thin lines) and for a 50 nm gold sphere (thick lines). The spectra have been normalized to their maximum values. Figure 1: Scattering cross section (thick solid line) and NFI in the forward direction (solid line), backward direction (dotted line), and at 90 (dashed line) respect to the incident The results shown in Fig. 2 confirm, through exact computations performed using the T-Matrix method, the well known red shift dependence upon the dimensions of the nanoparticle. We performed our computations for many different particle sizes. Here, for the sake of simplicity, we show only the scattering cross sections and NFI for a 30 nm gold sphere and for a 50 nm gold sphere. As the sphere size gets smaller, the red shift reduces as well, but never disappears. 22

23 In Fig. 3 we show the scattering cross section and the NFI for a dimer made of identical gold spheres each with a radius R=50 nm. The dimer geometry is such that the closest distance between the sphere surfaces is 4 nm. We computed the NFI at the central point of the hot spot and at a distance 5 nm from the sphere surface in the external region. We recall here that the hot spot is the region between the spheres where the field enhancement is the highest (see Fig. 4). Fig. 3 clearly shows that the red shift in the hot spot disappears, while it is still present in the dimer external region, in analogy with the single sphere case. compute the scattering cross section and the NFI for a dimer of gold spheres with different radii, R 1 =50 nm and R 2 =100 nm. Also in this case the closest distance between the surfaces of the two spheres is 4 nm (Fig. 5). Figure 4: Near-field intensity enhancement map for a silver dimer with R=75 nm. The closest distance between the surfaces of the two spheres is 5 nm. These results show that, when we break the symmetry of the dimer, the red shift appears also in the hot spot. The effect appears both for the dipole and for the quadrupole peak. Figure 3: Scattering cross section (thick solid line) and NFI (thin lines) at the central point of the hot spot (solid line) and at a distance d=5 nm from the sphere surface in the external region (dotted line) for a dimer of two identical gold spheres (R=50 nm). The spectra have been normalized to their maximum values. In Fig. 3 we show the scattering cross section and the NFI for a dimer made of identical gold spheres each with a radius R=50 nm. The dimer geometry is such that the closest distance between the sphere surfaces is 4 nm. We computed the NFI at the central point of the hot spot and at a distance 5 nm from the sphere surface in the external region. We recall here that the hot spot is the region between the spheres where the field enhancement is the highest (see Fig. 4). Fig. 3 clearly shows that the red shift in the hot spot disappears, while it is still present in the dimer external region, in analogy with the single sphere case. In order to demonstrate that the absence of the redshift in the hot spot is due to symmetry reasons, we Conclusions In conclusion, using the T-Matrix approach, we have shown how the near-field spectra of plasmonic nanoparticles are red-shifted compared to their far-field spectra. In order to generalize the results and to provide a systematic study of the relationship that exists between far-field and near-field quantities, it is necessary to extend the investigation to more complex structures, like large aggregates of spheres. We expect that taking into account the red shift effect can provide improvement in understanding and optimising surface-enhanced spectroscopies. This physical insight into the behaviour of plasmonic systems should be also useful for the practical design of plasmonic nanoparticles and nanostructures for applications of both fundamental and technological interest. 23

24 Figure 5: Scattering cross section (thick solid line) and NFI (dashed lines) at the central point of the hot spot region (solid line) for a dimer of R 1 =100 nm and R 2 =50 nm gold spheres. The closest distance between the surfaces of the two spheres is 4 nm. The spectra have been normalized to their maximum values. Acknowledgments I wish to thank R. Saija, M.A. Iatì, F. Borghese, P. Denti, P.G. Gucciardi, and O.M. Maragò for fruitful discussions and support. References [1] S. A. Maier, Plasmonics: Fundamentals and Applications, Springer (2007); [2] M.L. Brongersma, P.G. Kik, Surface Plasmon Nanophotonics, Springer Series in Optical Sciences, (2007); [3] L. Novotny and B. Hecht, Principles of Nano-Optics, Cambridge University Press, New York (2006); [4] B. J. Messinger el al., P. Rev. B 24 (1981) 649; [5] N. K. Grady el al., P. Chem. Phys. Lett. 399 (2004) 167; [6] A. S. Grimault el al., Appl. Phys. B: Laser Opt. 84 (2006) 111; [7] S. Bruzzone el al., J. Phys. Chem. B 110 (2006) 11050; [8] K. L. Kelly el al., J. Phys. Chem. B 107 (2003) 668; [9] G. W. Bryant el al., J. Nano Lett. 8 (2008) 631; [10] B. M. Ross el al., Opt. Lett. 34 (2009) 896; [11] J. Zuloaga and P. Nordlander, Nano Letters 11 (2011) 1280; [12] F. Borghese, P. Denti and R. Saija, Scattering from model nonspherical particles 2nd ed., Springer, Berlin (2007); [13] M.A. Iatì et al., MNRAS 322 (2001) 749; [14] C. Cecchi-Pestellini, A. Cacciola et al., MNRAS 408 (2010) 535. [15] M. A. Iatì, C. Cecchi Pestellini, A. Cacciola et al., JQRST 112 (2011) 1898; [16] R. Saija et al., Astrophys. J. 633 (2005) 953; [17] A. Cacciola et al., Astrophys. J. 701 (2009) 1426; [18] F. Borghese et al., Phys. Rev. Lett. 100 (2008) ; [19] R. Saija, et al., Opt. Exp. 17 (2009) 10231; [20] E. Messina, E. Cavallaro, A. Cacciola et al., ACS Nano 5 (2011) 905; [21] E. Messina, E. Cavallaro, A. Cacciola et al., J. Phys. Chem. C 115 (2011)

25 MASS QUADRUPOLE SPECTROMETRY APPLIED TO LASER- PRODUCED PLASMAS AND MICROWAVE IGNITED PLASMAS F. Di Bartolo a, *, L. Torrisi b,c, S. Gammino c, F. Caridi d, D. Mascali c,e, G. Castro c,f, L. Celona c, R. Miracoli c,f, D. Lanaia c, R. Di Giugno c,f. a) Dottorato in Fisica dell Università di Messina, Dip.to di Fisica, V.le F. Stagno D Alcontres 31, 98166, S. Agata- Messina, Italy b) Università degli Studi di Messina, Dip.to di Fisica, V.le F. Stagno D Alcontres 31, 98166, S.Agata-Messina, Italy c) INFN - Laboratori Nazionali del Sud, via S.Sofia 62, 95123,Catania, Italy d) Università degli Studi di Messina, Facoltà di Scienze MM.FF.NN., V.le F. Stagno D Alcontres 31, 98166, S. Agata- Messina, Italy e) CSFNSM, Viale A. Doria 6, Catania, Italy f) Università degli Studi di Catania, Dipartimento di Fisica e Astronomia, V. S.Sofia 64, Catania, Italy * Corresponding author, fdibartolo@unime.it Abstract The mass quadrupole spectrometry (MQS) permits the characterization of non-equilibrium and equilibrium plasmas obtained by means of laser ablation and microwave ionization. A Nd:Yag laser, 150 mj pulse energy, 3 ns pulse duration, operating at 1064 nm fundamental and 532 nm second harmonic wavelength, at intensities of the order of 1010 W/cm 2, in single pulse or at a repetition rate between 1 and 10 Hz, interacting with solid targets placed in high vacuum produces ablation with plasma formation. It is possible to analyze the ion and the neutral emission from plasma in the mass range amu with a mass resolution better than 1 amu and a sensitivity of the order of 1 p.p.m.. Moreover, it is possible to select the ion energy in the range 1 ev 1 KeV with an electric deflection filter. MQS allows to measure the temperature and density of the plasma, the relative ion and neutral amounts, the fractional ionization of the plasma, the elements and chemical compounds of the species participant to the plasma formation, the ion charge state, the ion energy distributions and the angular distribution of the emitted ions. Operating in repetition rate it measures the depth profile of peculiar elements in the ablated targets. Moreover, MQS permits also to characterize microwave ignited plasmas, obtained by means of microwaves at two different frequencies, 2.45 GHz (Magnetron) and GHz (TWT), axially launched inside the plasma chamber, where a strongly non uniform magnetostatic field exists (with a maximum value of 0.1 T), with two possible configurations depending on the used ion source (Plasma Reactor or VIS). In the regions under ECR (Electron Cyclotron Resonance) the X-B conversion is possible, the incoming electromagnetic extraordinary mode X is converted into a Bernstein wave B, i.e. an electrostatic wave which can propagate in an overdense plasma. Plasma density and temperature measurements, obtained with a Langmuir Probe and X-ray detectors, confirmed successfully the mode conversion and the formation of an overdense plasma. The similarities with non-equilibrium plasmas generated by laser ablation will be described along with the differences. Keywords: Mass Quadrupole Spectrometry, Laser- Plasma, Electrostatic Bernstein Waves, Plasma heating, Plasma vortex Introduction Mass spectrometry (MS) is an analytical technique to measure the mass-to-charge ratio of charged particles (m/q). A mass spectrometer is used to determine elemental composition, compounds and isotopes and, if there is also an energy filter, ion and neutral energy distributions. It permits to analyze both ions and neutrals, and is made up of three main parts: an internal ionization source, a mass analyzer and a detector [1]. It is known that intense pulsed laser beams, with an intensity of W/cm 2, can be focused on a solid material to produce ablation and formation of hot nonequilibrium plasmas, which have a duration of a few nanoseconds. The processes developed inside the lasergenerated plasma depend on many parameters, such as the laser characteristics, lens focalization, target composition, irradiation conditions, etc.. PLA obtained with ns lasers at high intensity generates hot plasma at the target surface, which expands in vacuum at supersonic velocity mainly along the normal to the irradiated target surface. A plasma characterization, in terms of temperature, density, energy of ejected particles, fractional ionization and charge state distribution, necessary to differentiate the plasma laser production, can be obtained. 25

26 Equilibrium plasmas are generated by means a Microwave Discharge Ion Source (MDIS), usually used to produce high intensity proton beams (above 50 ma). The operations of these devices is essentially based on the so called off-resonance discharge in a quasi-constant magnetic field B~0.1 T, obtained by launching microwaves with f= 2.45 GHz or GHz inside a metallic cavity of few cm of length and diameter. Such devices are density limited if the ECR is the only heating mechanism: the electromagnetic waves cannot propagate over a certain density, called cut-off density. To overcome the density limitations electrostatic Bernstein waves (EBW) heating [2] is an option. The EBWs are able to propagate in largely overdense plasmas, i.e. plasmas above the cut-off (n cutoff=3x10 10 cm -3 ), being absorbed at cyclotron harmonics [3]. EBW are created inside the plasma when a X wave, i.e. an extraordinary, E.M. wave, is converted from an E.M wave. It can be shown that X waves convert into EBW and ion waves at Upper Hybrid Resonance, when plasma frequency and frequency. 2 2 RF P C P being the 2 C being the cyclotronic We also used Cu, Al and Ta targets for our measurements. EQP spectra were analysed in order to determine the Cu ion energy distribution and separate the neutral component from the ionic component for Al and Ta targets. The fits of the experimental energy distributions were performed by means the Peakfit numerical code using the Coulomb-Boltzmann shifted function: (0.) f ( E) a) A 1 E 3 2 m ( kt ) 1 exp ( E Ek EC ) kt Vacuum chamber 2 MQS (1) Material and methods A Q-switched Nd:Yag pulsed laser operating at 1064 nm fundamental wavelength and at 532 nm secondharmonic wavelength, with 3 ns pulse duration and 160 mj maximum pulse energy, in single shot and repetition rate (1 and 10 Hz) mode, was employed for the measurements. The laser beam was focused, through a 50 cm focal lens placed in air, on the surface of a SiO 2 target, on which it produces a 0.5 mm 2 spot size, the laser-target interaction occurs inside a vacuum chamber, at 5 x 10-6 mbar pressure, and leads to the plasma formation. Ions and neutral particles are analysed by the MQS. Two types of mass quadrupole spectrometer have been employed: 1) a classical version of MQS, a Pfeiffer Vacuum Prisma Plus QMG 220, Mass Range amu, Mass resolution < 0.3 %, Sensitivity (SEM) 1 ppm; 2) a special electrostatic mass quadrupole spectrometer with an energy filter, Hiden EQP 300, Mass range amu, energy range 1 ev-1 kev, Sensitivity 1 ppm. The second type of mass spectrometer, differently with respect a classical MQS, permits to plot the energy distribution of neutral and charged species in the energy range 1 ev 1 kev. Figure 1 shows the experimental set-up (a) and the scheme of the Hiden EQP instrument (b). EQP is placed at 45º with respect to the incidence laser beam, i.e. along the normal to the target surface [4]. b) Laser system Fig.1 Scheme of the EQP instrument (a) and photo of the experimental set-up (b) 26

27 The characterization of equilibrium plasmas has been done by means a MDIS called VIS (Versatile Ion Source). The source body consists of a water-cooled copper plasma chamber (100 mm long and 90 mm diameter). VIS enable us to have purely off-resonance microwave injection (which is not possible using Plasma Reactor, another MDIS with a slightly different magnetic profile). Microwaves have been generated by using a conventional 300 W magnetron, able to generate 2.45 GHz microwaves, or a Travelling Wave Tube (TWT), able the generate microwaves from 3.2 to 4.9 GHz. The typical working frequency when using TWT was GHz. The measurements of temperature and plasma density have been carried out by using a movable Langmuir probe (LP). A Si-Pin X- ray detector has been used for the measurement of X rays spectra in different plasma conditions. The detector is able to detect X rays with energy greater than about 1 kev. Y : atoms Ar = Y : X atoms Si Ar Si (2) Results and discussions A. PLASMA LASER ABLATION (PLA) MQS can operate versus mass and versus time. In the first case we have a mass spectrum, where each of the detected peaks corresponds to a certain element or chemical compound. In the second case we obtain a MQS time spectrum, for some selected masses, which allows to know the relative elemental concentrations vs. the ablation time, permitting to plot the element depth profiles. The mass quadrupole spectrometer must be calibrated to know the exact number of atoms or molecules of the target detected during the laser ablation. In Figure 2 (a) the apparatus for the MQS calibration is shown [5,6]. In our calibration test, we employed a mixture of gas (50% Helium and 50% Argon) enclosed in a volume V 0 = 55.8 cm 3. The initial and final pressure of the gas in this volume are P i and P f, respectively, at a room temperature T = 22ºC. After that we open the Valve 3 in order to introduce a known gas quantity in the vacuum chamber, very near to the target position. We introduce a molecular number N = x of Argon and Helium atoms into the vacuum chamber. The calibration spectrum obtained by using the MQS permits to calculate the yield of Ar corresponding to 84 C. Afterwards we obtain the target spectrum which permitted us to calculate the yield of Si corresponding to 0.04 C. Calculating the ablation yield is possible by means the following proportion Fig.2 Scheme of the gas calibration apparatus. Thus the ablation yield resulted 3.18 x atoms of Si ablated for laser pulse. EQP Mass Spectrometer permits to obtain the ion energy distribution for a Cu target at two different laser energies, 40 mj and 160 mj, respectively. In the first spectrum the peak energy is 3eV while in the second one the peak energy is 17 ev. In figure 3 spectra obtained at energy of 160 mj are shown. Making a fit with a Coulomb-Boltzmann shifted function we can know two important parameters of a plasma, the temperature KT and the acceleration voltage V 0. The temperature is 2.9 ev and 8.9 ev, respectively. 27

28 kt ( ev ) 2 E( ev ) / 3 (3) where k is the Boltzmann constant. Eq. (2) gives 40 ev and 43.3 ev for Al and Ta neutral temperature, respectively. Ions are characterized by energy higher with respect to the neutrals, due not only to the thermal interactions between the plasma particles and to the adiabatic gas expansion in vacuum but also to the Coulomb interactions between the charged species. [7] Fig.3 Ion energy distribution and fit for a Cu target at a laser energy of 160 mj. B. PLASMAS MICROWAVES-GENERATED In the measurements performed with plasmas in equilibrium, we modified the position of the magnetic field with respect to the plasma chamber of VIS; in such a way, microwave injection takes place at different values of magnetic field. In figure 5 are shown. We use as reference B ECR. X ray were detected particularly in position D (B inj /B ECR =0.92, 1 kev spectral temperature). When the injection approaches Fig. 3 Ion energy distribution and fit for a Cu target at a laser energy of 160 mj. Assuming the peak energy to be representative of the distribution mean energy, we find that the mean energy for the only ions is higher with respect to the spectrum obtained detecting ions plus neutrals. At 150 mj the neutral plus ion mean energy is 85 ev and 115 ev for Al and Ta, respectively. At 150 mj the only ion mean energy is 95 ev and 120 ev for the two cases, respectively. Thus ions have mean energy higher with respect to neutral specie. The Peakfit deconvolution process applied to the ions plus neutral spectra separates the two components, ions from neutrals, and permits to extrapolate the neutral energy distribution by the difference between the ions plus neutral spectrum and the only ion spectrum. Fig. 4 shows the deconvolution spectrum obtained from an aluminium target. Deconvolution spectra report the neutral energy distribution (continuum line) obtained subtracting the only ion spectrum (full dots) to the ion plus neutral spectrum (open dots). The energy distributions of the neutral specie, obtained irradiating at 150 mj pulse energy, show mean energies, E, of about 60 ev and 65 ev for Al and Ta ablation, respectively. These energies are representative of the plasma temperature through the following relationship: Fig.4 Deconvolution spectrum reporting the neutral energy distribution (line) obtained subtracting to the only ion spectrum (fill dots) the ion plus neutral spectrum (open dots) for Al ablation. BECR, X rays tend to disappear and finally, at position A (Binj/BECR>1), no X rays were detected. These results show that the production of high energy X rays (T>1 kev) takes place only in case of underresonance discharge, that is the required condition to have UHR placed somewhere inside the plasma. Emittance measurements carried out in configuration A and in configuration D have shown a larger emittance in configuration D (0.207 πmm mrad) than in configuration A (only πmm mrad). The emittance depends by the magnetic field at 28

29 B [G] Activity Report 2011 Dottorato di Ricerca in Fisica, Università di Messina extraction Bext, the radius of extraction r, the ratio of ion mass in amu to charge state of the ion beam M/Q and the root square of ionic temperature [8,9]. kti r 0.032r Bext M / Q M / Q (4) a) A Magnetic field [G] ECR = 875 G B C D In our magnetic configurations emittance only depends on T i. Ionic waves are absorbed by ions through Landau damping. If T i are high we have a large emittance, therefore the more intense beam permitted by EBWs will be balanced and the brightness, that is the current intensity-emittance ratio, will not change and the ion source will not efficient. If T i are low we have an high current intensity, due to high density possible with EBWs, a low emittance and therefore an high brightness: the ion source will be efficient. However if T i are very high, in fact, value of 10 kev are possible due to the generation of vortex inside the plasma, we will get auto-accelerated ions, considering that in a common ion source ions have energy of ev or a fraction of ev [10] Position [mm] b) Conclusions The mass quadrupole analyser measures the mass-tocharge ratio (m/z) of the ions produced. A mass quadrupole spectrometer allows to determine main plasma parameters as the plasma temperature (KT), density (n), fractional ionization (f=n i /n t ), acceleration voltage (V 0 ) and electric field (E) [10]. EQP demonstrated high versatility to investigate on the amount and energy distribution of neutrals and allows to measure the plasma temperature starting directly from the neutral energy distribution. We will be performing measurements with the Mass Quadrupole Spectrometer Hiden EQP 300 to determine ions energy inside an equilibrium plasma in which a EBWs-heating mechanism occurs. In such a way we will compare ions energy obtained in non-equilibrium plasmas with that ones obtained in equilibrium plasmas to understand if EBW-heating mechanism allows to have an efficient ion source or high-energy autoaccelerated ions. Fig. 5 Position of Microwave injection with respect to off-resonance, in configuration B, C and D the injection occurs under-resonance (a); X ray detected at different position of magnetic field (b). References [1] E. De Hoffmann and V. Stroobant, Mass Spectrometry: Principles and Applications, 3rd ed.wiley (2007). [2] Ira B. Bernstein., Phys. Rev., 109, (1958) 10; [2] Ira B. Bernstein., Phys. Rev., 109, (1958) 10; [3] K. S. Golovanivsky et al., Phys. Rev. E 52, (1995) 2969; [4] L. Torrisi et al., NIM B266 (2008) 308; [5] L Torrisi. et al. Rad. Eff. and Def. in Solids, 161(1) (2006) [6] F. Di Bartolo et al. Nucleonika (2011), submitted [7] L. Torrisi et al., Appl. Surf. Sc., 252 (2006) 6383; [8] D. Mascali et al., NIM A, 653 (2011) 11; [9] G. Castro et al., ICIS 11, Rev. Sc. Instr., (2011), in press; [10] K. Nagaoka et al., Phys. Rev. Lett.89 (1992) 7. 29

30 30

31 FUSION REACTIONS IN COLLISIONS INDUCED BY LI ISOTOPES ON SN TARGETS M. Fisichella a,b, A. Di Pietro b, A. Shotter c,d, P. Figuera b, M. Lattuada b,e, C.Marchetta b, A.Musumarra b,e, M.G. Pellegriti b,e, C.Ruiz c, V. Scuderi b,e, E.Strano b,e, D.Torresi b,e, M.Zadro f a) Dipartimento di Fisica, Università di Messina, Messina, Italy b) INFN- Laboratori Nazionali del Sud and sezione di Catania, Catania, Italy c) TRIUMF, Vancouver, Canada d) School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK e) Dipartimento di Fisica ed Astronomia, Università di Catania, Catania, Italy f) Ruđer Boŝković Institute, Zagreb, Croatia Abstract For investigating the role of the Q-value for neutron reaction in fusion reaction induced by weakly bound nuclei, fusion reactions of lithium isotopes with a combination of different Sn isotopes have been proposed, by using an activation technique. 6 Li+ 120 Sn and 7 Li+ 119 Sn have been already performed. I will show here the result of the preliminary analysis of these two reactions. Introduction Recently more and more experimental evidences have been observed concerning the enhancement of the subbarrier fusion cross section due to neutron transfer, both in reaction with stable nuclei [1,2] and especially in reaction with weakly bound nuclei[3]. In particular the enhancement seems to be related to sign of the Q-value for neutron transfer. A new mechanism has been proposed [4] for the sub-barrier fusion of weakly bound nuclei, in which an intermediate rearrangement of valence neutrons with positive Q-value may lead to a gain in kinetic energy of the colliding nuclei and, thus, to enhancement of the barrier penetrability and therefore of the fusion crosssection. To investigate the role played by the coupling to transfer channels having positive Q-value, we have proposed to study the fusion of lithium isotopes with a combination of different Sn isotopes. The systems which would like to study are 6 Li+ 120 Sn, 7 Li+ 119 Sn, 8 Li+ 118 Sn and 9 Li+ 117 Sn. All these reactions lead to the same compound nucleus but are characterized by different Q- value for neutron transfer. The fusion cross section are measured by using an activation technique where the radioactive evaporation residues produced in the reaction are identified by the X-ray emission which follows their electron capture decay. The 6 Li+ 120 Sn, 7 Li+ 119 Sn have been already performed at LNS, Catania. The 8 Li+ 118 Sn, 9 Li+ 117 Sn will be performed at TRIUMF, Canada. Experimental technique As in our previous experiment [5,6], we proposed to measure the fusion excitation function by using an activation technique, based on the off-line measurement of the atomic X-ray emission following the electron capture decay of the evaporation residues produced in the reactions. The direct detection of E.R., produced in the collision of a low energy light projectile onto a medium target is not possible since the largest fraction of E.R. produced will not come out from the target owing to the their low kinetic energy. But by choosing a suitable target, with the help of statistical model calculation, it is possible to obtain E.R. unstable against E.C. decay and so it is possible to identify the E.R. by looking at their X rays. This technique consists of two steps: the activation of the target and the off-line X-ray measurement. The activation step of the measure has been performed in the CT2000 scattering chamber at LNS with the 6 Li and 7 Li beams delivered by the SMP Tandem Van Graaff accelerator. A stack of four Sn targets followed by Nb catchers were irradiated with the Li beam. The catchers were needed in order to stop the residues emerging from the previous target and to slow down the beam, thus increasing the average difference in beam energy for the different targets. Possible reactions induced by the beam on the 93 Nb catchers do not represent a problem since the X-ray energies are different to the ones corresponding to reactions on 64 Zn. By activating a stack of targets it is possible to extract the cross section at different energies without changing the beam energy thus reducing the beam time needed to perform an excitation function measurement with the very low intensity radioactive beams. This technique is for this reason very useful in the case of radioactive beam. Two irradiation runs are been performed for each system: 1) A first stack was irradiated with 25 MeV 6,7 Li beam of about pps for about three hours. 2) A second stack was irradiated for about three days (to optimize the 124 I production at low energy) with 21 MeV 6,7 Li beam. By using these stacks, a centre of mass energy range between 16 MeV< E c.m. < 24 MeV.To extract the production cross section it is necessary to measure the beam current as a function of time for the entire duration of the activation step. This operation has been performed using two Surface Barrier Silicon Detector collecting the particles scattered by a thin gold foil placed before the 31

32 stack on the beam line. Since the scattering is of Rutherford type, the beam intensity can be extracted by his well-known cross-section formula. With the two symmetrical monitors it is possible to reduce systematic errors due to mechanical misalignments. After the irradiation, the E.R. emitted from the different targets (together with the corresponding catcher) were measured off-line using Pb shielded large area Si(Li) detectors. Each measurement was repeated in order to measure the activity as a function of time. For determining the fusion cross section it is really important to know the intrinsic efficiency of the detector. We measured the efficiency of our detector using some calibrated sources, because in the energy range, in which we are interested in, the efficiency for these detector is strongly dependent from the energy. PRELIMINARY RESULTS Typical X-ray spectra measured off-line for the reaction 6 Li+ 120 Sn is shown in figure 1, where the peaks corresponding to K α and K β X-ray emission of Sb and I are shown. The K β emission represents about 15% of the total k X-rays emission. In the present experiment, the analysis was performed only on the K α lines. Figure 1 Typical X-ray spectra measured off-line for the reaction 6 Li+ 120 Sn at 25 MeV. It is possible to distinguish Sb and I peaks. From the X-ray energies we can only identify different elements but not different isotopes. We can characterize the isotope by following the time behavior of the X-ray lines, characteristic of each element, and by fitting it using the known half-lives. Plotting these data on a semilogarithm graph (that is ln A vs t) should give a straight line of slope -λ, the decay constant.in figure 2 a typical activation curve for the reaction 6 Li+ 120 Sn at 25 MeV is shown. It is possible to observed three different slope which characterize this curve. Each slope correspond to a different I isotope produced in the reactions. In particular one may observe the contribution of 123,124,125 I. Figure 2 Activity curve for the I isotopes, obtained for the reaction 6 Li+ 120 Sn at 25 MeV. By fitting the activation curves for each E.R. one obtains the A 0exp, that is its activity at the end of the irradiation time, which is another important quantity for the measurement of the fusion cross section. Future perspectives The fusion cross section is given by the following relation: A0exp (1) N N K where 0exp 0 i t 0 T A represent the number of compound nuclei at the end of the irradiation time. As it was told before, A is obtained from the fit of the activation 0exp curve (figure 2). The term is then corrected for the fluorescence probability ( K ) and for the detector efficiency ( T ), which is determined experimentally by using calibrated sources. N t is the number of target atom per cm 2 and N t is the incident beam current (i.e. the number of incident particles), which is determined by analyzing the Rutheford scattering data. The next step of my analysis will be just the determination of N i, and then the measurement of the fusion cross section for the two reaction already performed. From the comparison of the fusion cross sections of all the systems it will be possible to investigate on the possible role of the Q-value for neutron transfer in the fusion reaction. References [1] Trotta et al., Phys.Rev. C 65, (2002); [2] Stefanini et al, Phys.Rev. C (2006); [3] Penionzhkevich et al., Phys. Rev. Lett (2006); [4] Zagrebaev et al., Phys. Rev. C (R) (2003); [5] Di Pietro et al. Phys.Rev.C 69 (2004) ; [6] Di Pietro et al. Europhys.Lett. 64 (2003)

33 PARTICLE CORRELATIONS AT INTERMEDIATE ENERGIES AND THE FARCOS PROJECT T. Minniti 1,2 and Farcos/Chimera collaboration 1Dipart. di Fisica, Università di Messina, v.le F. D Alcontres 31, S. Agata, Messina, Italy. 2INFN-Gruppo collegato di Messina, Messina, Italy. Corresponding Author: tminniti@unime.it Keywords: Particle correlations, correlation functions. Abstract The study of correlations between two or more particles emitted during a nuclear reaction provides tools to explore the space-time properties of the reaction and spectroscopic features of produced exotic clusters [1]. Correlation imaging techniques are known to provide space-time snapshots of particle emitting sources [1]. These sources allow one to extract the size of emission regions in properties of nuclear matter produced during the reaction. Moreover, two-nucleon correlations probe the relative emission times of preequilibrium protons and neutrons that are strongly affected by the symmetry energy and its symmetry dependence [2]. Studies with particle correlators used in heavy-ion collision experiments conducted at MSU and at the LNS will be presented and discussed. Future improvements of these studies require a new array of telescopes with high angular and energy resolution coupled to a 4 detector necessary to perform better exclusive measurements. In order to address these topics a new project has been started at the INFN, Sezione di Catania and Laboratori Nazionali del Sud. The name of this project is FARCOS (Femtoscope ARray for COrrelations and Spectroscopy) and it consists of building an array of double-side silicon strip detectors and CsI(Tl) crystals characterized by high angular and energy resolution. Farcos will represent an important scientific upgrade of the physics studies with the Chimera detector at INFN. The array can be used as a correlator to be coupled to existing 4 detectors such as Chimera at LNS. Such as 4 device is necessary to characterize the collision events (determination of impact parameter, reaction plane, fragment yields and spectra) while Farcos is used in coincidence to measure correlation functions. The Farcos array will be characterized by a compact electronics and a geometric flexibility that will also allow it to be transported to different laboratories, depending of the beam/target combination to be studied, that to be adapted to different 4 detector environments (Chimera at the LNS, Indra at GANIL, etc.). These features and their impact in future programs of Farcos+Chimera experiments at the LNS of Catania will be described. These will involve experiments to study decay channels of unbound and exotic nuclei produced in both direct reactions with radioactive beams and with heavy-ion collisions at the LNS of Catania [3,4]. In the second case, several unbound states are indeed produced during the dynamical evolution of heavy-ion collisions and one can study some spectroscopic properties such as their sequential decays proceeding through the production of sequences of unbound nuclei or cluster and nuclear molecular states [4]. Introduction The study of correlations between particles emitted during a collision between two heavy ions provides information about the space-time properties and quantitative understanding of reaction dynamics. This in turn depends on the details of the nuclear interaction and the equation of state (EoS) of nuclear matter. The future radioactive beam facilities as well as the existing stable beam laboratories will allow studying these problems with higher sensitivity to the isospin degree of freedom thanks to the capability of accelerating highly N/Z asymmetric beams at intermediate energies. In this respect, detectors capable of detecting all reaction products on an event-by-event basis and measure their reciprocal correlations are mandatory [1,2]. Different observables need to be measured over a large solid angle coverage with high energy and angular resolution. The solid angle coverage guarantees a characterization of the collision event. The energy and angle resolution are important in order to measure the momentum vectors and kinetic energies of the detected particles and explore their correlations. Recent implementation of pulse-shape identification techniques promise to provide unique capabilities [3-5] that will allow studying nuclear dynamics even at low energies at facilities such as Spiral2 and Spes [6]. In this contribution we present the physics cases for the construction of a detector array meant to measure correlations between particles and fragments in coincidence with large solid angle arrays. The name of the project is Farcos, standing for Femtoscope ARray for Correlations and Spectroscopy. It is expected to address topics in femtoscopy via intensity interferometry and spectroscopy with radioactive beams. 33

34 Dynamics and two-particle correlations Heavy-ion collisions allow one to explore the properties of nuclear matter under extreme conditions. A clear understanding of the dynamics of heavy-ion collisions is required. Particles are emitted at different stages that are difficult to isolate. It is therefore important to disentangle particle and fragment emitting sources. Where and when are fragments produced? Understanding dynamics in heavy-ion collisions requires tracing-back particle and fragment emitting sources. Such challenge can be accomplished by using two-particle correlation function known to be sensitive to the space-time features of nuclear reaction mechanisms [7]. The shape of correlation functions probe important transport properties of nuclear matter and the density dependence of symmetry energy in the equation of state. Figure 1. Left panel: Two-proton correlation functions measured in Ne+Au collisions at E/A=75 MeV. See Ref. [8] for details. Right panel: emitting source functions extracted by imaging. Two-proton correlation functions, 1 Rq ( ), is defined as the ratio between the two-proton coincidence and uncorrelated spectra, Y ( q ) and coin Yunco ( q ), respectively. q is the relative momentum between two protons in Y coin and Y unco spectra. Uncorrelated proton pairs are usually constructed by coupling protons from different events. Fig. 1 shows such a correlation function in the case of N+Au collisions at E/A=75 MeV [8]. The peak at q=20 MeV/c is due to the nuclear interaction between the two protons and determines the spatial extent of the emitting source, S(r), defined as the probability of emitting two protons with a relative distance r recorded at the time when the second proton is emitted. Imaging techniques [8 and Refs. therein] have been successfully used to extract the emitting source function from the measured correlation function. This images represent sort of space-time pictures of the emission [7-9]. The right panel of Fig. 1 shows the source functions, S(r), extracted from the correlations represented on the left panel. The source function not only provides information about the size/volume of the emitting source, but also allows us to estimate the relative contributions between fast dynamical pre-equilibrium sources and slowly evaporating sources characterizing the later thermalized stages of the reaction [8]. This sensitivity of R(q) to the space-time features of the reaction becomes very useful as tool to explore transport properties of nuclear matter. Indeed microscopic transport models have shown sensitivity to the nucleon-nucleon (NN) collision cross section in the nuclear medium [9] and to the density dependence of the symmetry energy [10]. Such research program requires also the difficult task of measuring p-p, n-p and n-n correlation functions in the same experiment [10]. Coupling charged particle and neutron detectors is also a priority in this respect. Extending these measurements to fragment-fragment correlation functions allows one to extract space-time information about the stage of heavy-ion collisions when nuclear matter at low density breaks-up into complex fragments possibly indicating the occurrence of a phase-transition [11] and carrying important signatures of the effects of the symmetry energy and its density dependence. The possibility of measuring fragment correlation functions is further enriched by the introduction of powerful pulse-shape capabilities that would allow identifying fragments at low kinetic energies [3,4]. These fragments can be identified only by a detailed study of the shape of the signal induced by their passage through the detector [2-4]. Another important application of intensity interferometry is represented by the study of correlations between unlike light particles, such as proton-alpha, deuteron-alpha, deuteron- 3 He, etc. [7]. An extended study of all these correlation functions would allow a reconstruction of several emitting sources in the same reaction. These light particle correlations are usually characterized by the presence of several resonances and a precise measurement of their position and shape is mandatory in order to probe their emitting sources. High angular resolution is thus a key feature of an array meant to perform correlation measurements between light particles. Correlation functions as a spectroscopic tool During the dynamical evolution of the system several loosely bound nuclear species are produced for a very short time and decay. Their unstable states can be identified and explored by detecting all the products of their decay in coincidence. A typical example of this type of analyses has been shown in Ref. [12] where p- 7 Be correlation functions were measured in order to study unbound states in 8 B nuclei and probe their spins 34

35 [12]. In a more recent experiment, three- and fourparticle correlation functions have been used to study highly lying unbound states in 12 C and 10 C nuclei [13]. Three-alpha particle correlation functions can be used to study the decay of internal states in 12 C. While twoalpha-two-proton correlation functions probe 10 C decay. In the case of 12 C these correlation studies allow one to disentangle the direct decay into three alpha particles from the sequential decay into 8 Be+alpha with a subsequent decay of 8 Be into two alphas. In the case of 10 C studies one can identify the decay sequence of unbound states that produce intermediate states in 6 Be, 8 Be and 9 B [13]. The techniques reported on Ref. [13] show that one single heavy-ion collision can provide access to some spectroscopic information of exotic unbound states. The availability of very proton-rich beams at the future exotic beam facilities can enhance the possibility of producing even more exotic resonances and study their decay properties. Figure 2. Left panel: Schematic view of the expected design of Farcos telescopes. Right panel: Coupling of the Farcos array to the Chimera detector at the LNS of Catania. Required array features Based on the physics cases outlined above, we plan to build an array of silicon strip and CsI(Tl) telescopes to be coupled to large detector arrays such as Chimera@LNS-Catania. A minimum of about 15 telescopes is required in order to address a number of physics cases as outlined above. However a larger solid angle coverage would significantly increase the scientific reach of the project. The array will have a large geometric flexibility. Silicon strip detectors with thicknesses of 300 and 1500 m (6.4 x 6.4 cm 2 ) will be followed by 6 cm long CsI(Tl) crystals arranged in a square configuration 2 x 2 (each crystal will have a front face of 3.2 x 3.2 cm 2 ). This array will provide an angular resolution up to about 0.1 o at a distance of 1 m from the target. The left-end side of Fig. 2 shows a schematic view of the basic telescope. The geometry flexibility of the telescopes is expected to allow the use of an additional silicon strip detector aimed at lowering the identification threshold. Low thresholds will also be attained with pulse-shaping techniques [3-5]. Silicon ntd solutions are also under consideration to improve pulse-shaping capabilities. The required electronics will need to address the goal of obtaining high resolution, high dynamic ranges and high flexibility (programmability) in order to identify light and heavy fragments. Due to the large number of channels that will be employed in the array, an integrated electronics solution will be required. The right-end side of Fig. 2 shows a possible arrangement of the array inside the Chimera reaction chamber at the LNS of Catania. The use of the array in studying correlations between charged particles and neutrons is also envisioned and will require a specific study on the materials required in order to couple Farcos telescopes to neutron counters. The high flexibility of the array will certainly allow further applications at the future radioactive beam facilities, especially when studying reactions induced by proton-rich beams. These beams will allow studying correlations between charged particles emitted by short-lived exotic nuclei abundantly produced close to the proton-drip line (two- and multi-proton emitters, etc.). Also, studying direct reactions induced by radioactive beams, such as (p,d), (d,p) etc. reactions, will be possible due to the envisioned high energy and angular resolution and to the geometric flexibility [14]. References 1. J. Pouthas et al., Nucl. Instr. and Meth. A 357 (1995) 418; 2. A. Pagano et al., Nucl. Phys. A681 (2001) 331c; 3. A. Alderighi et al., IEEE Trans. on Nucl. Sci. 52, (2005) 1624; 4. L. Bardelli et al., Nucl. Instr. Meth. A 605 (2009) 353; 5. L. S. Barlini et al., Nucl. Instr. Meth. A 600 (2009) 644; G. Verde et al., Eur. Phys. J. A 30 (2006) 81; 8. G. Verde et al., Phys. Rev. C 65, (2002); 9. G. Verde et al., Phys. Rev. C 67, (2003); 10. L.W. Chen et al., Phys. Rev. Lett. 90, (2003); 11. L. Beaulieu et al., Phys. Rev. Lett. 84, 5791 (2000); 12. W.P. Tan et al., Phys. Rev. C 69, (2004); 13. F. Grenier et al., Nucl. Phys. A 811, 233 (2008) ; 14. E. Pollacco et al., Eur. Phys. J. A 25, s01, (2005). 35

36 36

37 INVESTIGATION ON PSEUDOSCALAR MESON PHOTOPRODUCTION BY ELECTROMAGNETIC PROBE M. Romaniuk a,b,c,*, V. De Leo a,b, F. Curciarello a,b, G. Mandaglio a,b, G. Giardina a,b a) Dipartimento di Fisica, Università di Messina, I-98166, Messina, Italy b) INFN- Sezione Catania, I-95123, Catania, Italy c) Institute for nuclear Research, National Accademy of Science of Ukraine, Kiev, 03680, Ukraine * mromaniuk@unime.it Abstract The Dalitz decay, second most common decay mode of 0 e e, with probability , was studied. Dalitz and double Dalitz decays are of interest because they can be exploited to perform a measurement of the electromagnetic form factor of the decaying meson. Such mode of pions decay is a prominent quantity in many sub-fields of particle physics, such as chiral perturbation theory and for g-2 physics. Performed analysis of the GRAAL data and prospective for BGO-OD for interested channel. Introduction The studding of the nucleon structure is one of primary interests in the strong interaction physics and has been the subject of experimental and theoretical studies for several decades. To describe strong interactions we are using Quantum Chromo Dynamics (QCD) the formal theory of the colour interactions between quarks. In the high energy regime (α s <<1) common tool to perform investigation at QCD is perturbative approach. In low energy regime( where α s 1), which is typical of the nucleon and its resonances, it is not possible to use perturbative approach. Using different effective degrees of freedom of the nucleon one could obtain different nucleon resonance spectra. But up to now exist an open problem with missing resonances: not all predicted states was observed. The dominant decay channel for nucleon resonances is the strong decay with single or multi meson emission. The excited states have strong overlapping between the excitation curves of resonances whose masses can differ of tens of MeV. Tools for the study of nucleon resonances is πn experiments by electro-magnetic probe. The availability of high intensity and high duty cycle electron and photon facilities open new possibilities for the study of baryon resonances using electromagnetic probes. These provide information on the resonances and nucleon wavefunctions through the measurement of the helicity amplitudes, i.e. the electromagnetic couplings between nucleon ground state and initial states. In addition electroproduction also allows us to explore baryon structure for different distance scales by varying the photon virtuality. Nowadays electro-excitation processes are a fundamental tool to pursue these studies. Meson Photoproduction Experimentally, the density of states of the baryon resonances in the mass region above 1.8 GeV is much Figure 1: Total photoabsorption cross section and exclusive cross sections for single-meson and multimeson production. (a) Total, pπ 0, p p '; (b) total, K +, K +, K 0 ; (c) p,p, p,,, ; (d) pπ + π -, pπ 0 π 0, pπ 0 pπ + π - π 0, pk + K -. smaller than expected. A reason might be [1, 2] that these missing resonances decouple from the πn channel. Then they escape detection in πn elastic scattering. These resonances are expected to have no anomalously low helicity amplitudes; then they must show up in photo-production of multiparticle final states. From the electroproduction of baryon resonances helicity amplitudes, form factors, and generalized polarizabilities (inaccessible to πn scattering) can be 37

38 extracted. Intense experimental and theoretical efforts have been devoted to determinations of the E2/M1 (electric quadrupole versus magnetic dipole) and C2/M1 (longitudinal electric quadrupole versus magnetic dipole) ratio for the N (1232) transition amplitude. The total photoabsorption cross section shown in Fig. 1 exhibits a large peak ( b) due to (1232) production, shows some structures in the second and third resonance regions, and levels off at about b at a few GeV [3]. Polarization observables The differential cross section for electroproduction of pseudoscalar mesons off nucleons is given by the product of the flux of the virtual photon field with longitudinal (L) and transverse (T) polarization and the virtual differential cross section, which depends on six response functions (R i = R T, R L, R TL, R TT, R TL', R TT' ). The response functions depend on two additional indices characterizing the target polarization and the recoil polarization of the final-state baryon. Thanks to polarization observables it is possible to separate overlapping resonances. The Gerasimov-Drell-Hearn sum rule The photoproduction cross section depends on the helicity of proton and photon. The Gerasimov-Drell- Hearn (GDH) relates the integral over the helicity asymmetry of the total absorption cross section for circularly polarised photons on a longitudinally polarised nucleon target to the nucleon anomalous magnetic moment k, the spin S and the mass M: 2 p a 2 2 IGDH d 4 k S 2 th e M (1) where ζ p and ζ a are the total absorption cross sections for parallel and antiparallel relative spin configurations respectively, and the cross section is weighted by the inverse of the photon energy. The lower limit of the integral, th, corresponds to the inelastic threshold of the reaction which, in the case of the nucleons, is the pion photoproduction threshold. Measurements of the helicity difference on exclusive final states provide an important input to partial-wave analyses. fact that it provides information on the semi off-shell transition form factor F 0 * in the time-like region, and more specifically on its slope parameter a. The muon g 2 is one of the most precisely measured and theoretically best investigated quantities in particle physics. Our interest in very high precision measurements is motivated by eagerness to exploit the limits of our present understanding of nature and to find effects which cannot be explained by the established theory. More than 30 years after its invention this is still the SM of elementary particle interactions, a SU(3) c SU(2) L U(1) Y gauge theory broken to SU(3) c U(1) em by the Higgs mechanism, which requires a not yet discovered Higgs particle to exist. As important as charge, spin, mass and lifetime, are the magnetic and electric dipole moments which are typical for spinning particles like the leptons. Both electrical and magnetic properties have their origin in the electrical charges and their currents. Magnetic monopoles are not necessary to obtain magnetic moments. On the classical level, an orbiting particle with electric charge e and mass m exhibits a magnetic dipole moment given by L e L 2m (2) where L mr v is the orbital angular momentum. An electrical dipole moment can exist due to relative displacements of the centers of positive and negative electrical charge distributions. For a particle with spin the magnetic moment is intrinsic and obtained by replacing the the angular momentum operator L by the spin operator S (3) 2 where is the Pauli spin matrices. Thus, generalizing the classical form (2) of the orbital magnetic moment, one writes m gq 0 (4) 2 Daliz decay Dalitz decay, e e is the second most important decay channel of the neutral pion with a branching ratio of (1.198±0.032)%, while the dominant decay mode, has a branching ratio of ( ± 0.032)%. The interest of the Dalitz decay lies in the where 0 e 2 m, Q is the electrical charge in units of e, Q= 1 for the leptons (l = e, μ, η ), Q=+1 for the antileptons and m is the mass. The equations define the gyromagnetic ratio g (g-factor) quantity exhibiting important dynamical information about the leptons. 38

39 The deviation from the Dirac value g /2=1, obtained at the classical level, is anomalous magnetic moment: gl 2 a (5) l 2 Figure 2. Spin precession in the g 2 ring ( 12 /circle). The measurement of aμ is illustrated in Fig. 2 [6]. When polarized muons travel on a circular orbit in a constant magnetic field, then aμ is responsible for the Larmor precession of the direction of the spin of the muon, characterized by the angular frequency a eb a m (6) From comparison standard model theory and experiment one could obtain: exp th 10 a a (7) Is there new physics? The various components of the g-2 is QED, weak contribution, hadronic vacuum polarization and hadronic light by light. The most problematic set of hadronic corrections is that related to hadronic lightby-light scattering. Such contributions can be dramatically enhanced and thus represent an important contribution which has to be evaluated carefully. The problem is that even for real-photon light-by-light scattering, perturbation theory is far from being able to describe reality, showing sharp spikes of π 0, η and η' production, while pqcd predicts a smooth continuum. Experimental set-up The new experimental setup of the recently established BGOOD collaboration consists of the combination of an open-dipole forward spectrometer and the BGO ball of the former GRAAL collaboration to cover the central angular region. This configuration is ideally suited to investigate the photoproduction of multiparticle final states with mixed charges. In addition it will allow nucleon polarization measurements in single-meson photoproduction. Due to the excellent forward acceptance it opens the possibility to investigate vector-meson production in order to understand the reaction mechanism and the role of resonances. The BGOOD collaboration presently includes individuals and groups from Germany (Bonn), Italy (Rome, Frascati, Pavia, Messina), Russia (Gatchina, Moscow), UK (Edinburgh, Glasgow) and Ukraine (Kharkov), and is open for further extension. The experimental set-up consists of a large 90 ton dipole magnet, tracing detectors, two scintillating fiber detectors, MOMO and SciFi2 (to allow for momentum reconstruction of charged particles bent through the magnetic field), an aerogel Cherenkov detector (discriminates pions against protons and particularly improves the K ± -identification substantially), a timeof-flight (TOF) detector (provides flight-time measurements for charged particles and neutrons), the BGO Ball hermetically encloses the target (polar angular range degrees). The BGO (Bi 4 Ge 3 O 12 ) Ball is made of 480 truncated pyramidal crystals, mechanical structure consists 24 carbon fibre baskets (each containing 20 crystals) and external steel support. The baskets keeps crystals separated, mechanically and optically. The photomultiplier tubes (readout of the crystals) coupled directly to the crystals. By this way obtains an excellent energy resolution also at low energies. The target cell is a 4 cm diameter aluminum cylinder, closed by thin mylar windows at the two sides, filled by liquid Hydrogen (H 2 ) or Deuterium (D 2 ). The target placed along the photon beam direction and surrounded by BGO Ball hermetically. The hydrogen/deuterium gas is cooled down by the helium using heat exchangers and liquefied inside the cell. The working temperature of the liquid Hydrogen or Deuterium is about 17 K and 22 K respectively. 39

40 Recent relevant results of our analysis Figure 3. The invariant γ γ mass spectrum obtained with the Crystal Ball detector. By analysing the experimental data of Graal experiment we identify the invariant mass of π 0 and η from Daliz decay e + e -. About η': it is not possible to measure with enough statistics because at Graal the energy E is up to 1.5 GeV, only 50 MeV over the threshold of η' production. By looking the invariant mass obtained without any cuts application, the meson reconstruction by two charged particle and one neutral particle in the BGO is strongly dominate by π + π - π 0 or similar multiple pion channels (Fig.4). Finally by applying our cuts, we was able to measure and distinguish the π 0 and η events, see the reconstructed invariant mass in Fig.5. The statistics available at Graal is not enough to extract the observables presented in this measurement, but this work result very promising at BGO-OD for the higher intensity of the beam and the larger solid angle of detection available in the new experiment. Figure 4. Energy balance (all quantity was directly measured) and invariant mass in the final state: no cut (red), a cut on Fermi momentum of Spectator in Deuteron Target lower than 0.2 GeV/c and on Neural Network variable higher than 0.8 were applied (black). We are interesting in the channel with pseudoscalar meson p PS p, wich decay to PS e + e - or PS e + e - e + e -. Where pseudoscalar meson (π 0, η and η') as much as possible near threshold. Our goal is to identify (PS) thanks to the missing mass of the system ( p p') and then study the PS decay product (Fig.3). Figure 5. Reconstructed invariant mass of π 0 and η. References [1] Koniuk, R., and N. Isgur, Phys. Rev. D 21 (1980) 1868; [2] Koniuk, R., and N. Isgur, Phys. Rev. Lett. 44 (1980) 845; [3] Klempt E. and Richard J.-M.: Baryon spectroscopy, Rev. Mod. Phys., Vol. 82 (2010 ) No. 2, 1-59; [4] Gerasimov S. B., 1966, Sov. J. Nucl. Phys. 2, 430, Yad. Fiz. (1966) 2, 598; [5] Drell, S. D., and A. C. Hearn, Phys. Rev. Lett. ( 1966)16, 908; [6] F. Jegerlehner, A. Nyffeler, Physics Reports 477 (2009)

41 STUDY OF NUCLEAR EQUATIONS OF STATE: THE ASY-EOS EXPERIMENT AT GSI S. Santoro a,b for ASY-EOS collaboration a)dottorato in Fisica dell Università di Messina, Dip.to di Fisica, V.le F.S. D Alcontres,98166 S. Agata-Messina, Italy b) INFN-Gruppo Collegato di Messina, Messina, Italy The study of the symmetry energy at nuclear densities up to few time over the saturation value (~ 0.15 fm -3 ) constitutes an important task to improve knowledge for the physics of heavy ion collisions (with stable and radioactive beams) and astrophysics due to the strict link with neutron stars studies. The AsyEos collaboration has proposed an experiment at GSI (S394) in order to study the nuclear collisions 197 Au Au, 96 Ru + 96 Ru and 96 Zr + 96 Zr at 400 MeV/nucleon incident energy with the SIS accelerator. In this experiment the Land neutron detector, the Aladin ToFWall, the forward part of the Chimera device and the Si-CsI Krakow array have been used with the goal to study the neutron and protons elliptic flows in an optimized experimental conditions and with improved statistics respect to the previous Fopi experiments devoted to measure the observables that we want to study. The reaction Au+Au has been successfully performed in May We will present, after a brief summary of the main motivations of the experiment, the first results relative to the response of various devices used. In particular the preliminary results of the charge high identification obtained by means fastslow technique in the Chimera CsI detectors will be shown. Introduction A key question in modern nuclear physics is the knowledge of the nuclear Equation Of State (EOS) and, in particular, of its dependence on density and on asymmetry, i.e., on the relative neutron-to-proton abundance [1, 2, 3, 4]. The EOS can be divided into a symmetric term (i.e., independent from the isospin asymmetry I N N Z Z, where N and and Z are the numbers of neutrons and protons, respectively) and an asymmetric term (also known as the symmetry energy) that is proportional to the square of the isospin asymmetry I [3,4,5]. Measurements of isoscalar collective vibrations, collective flow and kaon production [1,6,7] in energetic nucleus-nucleus collisions have constrained the behaviour of the equation of state of isospin symmetric matter for densities up to five times the saturation density ρ 0. On the other side, the EOS of asymmetric matter is still subject to large uncertainties. Besides the astrophysical interest, e.g. neutron star physics and supernovae collapse [8,9], the density dependence of the symmetry term is of fundamental importance for nuclear physics. The thickness of the neutron skin of heavy nuclei reflects the differential pressure exerted on the core [10] and the strength of the three-body forces, an important ingredient in nuclear structure calculations [11], represents one of the major uncertainties in modeling the equation of state at high density [1,12]. Moreover, properties of exotic nuclei, i.e., nuclei far away from stability valley, and the dynamics of nuclear reactions rely on the density dependence of the symmetry energy [3,4]. In the last decade, measurements of the Giant Monopole [13], Giant Dipole [14] and Pygmy Dipole [15] resonances in neutron-rich nuclei, isospin diffusion [16,17], neutron and proton emissions [18], fragment isotopic ratios [17,19,20] and isospin dependence of competition between deep-inelastic and incomplete fusion reactions [21] have provided initial constraints on the density dependence of the symmetry energy around and below saturation density ρ 0. It results that the best description of experimental data is obtained with a symmetry sym 2 / 3 sym energy S(u) Ckin (u) Cpot (u) with in the range [17] ( u / 0 is the reduced nuclear density). In the near future, extensions of these measurements with both stable and rare-isotope beams will provide further stringent constraints at subsaturation densities. In contrast, up to now, very few experimental constraints exist on the symmetry energy at supra-saturation densities ( u 1). This is the domain with the greatest theoretical uncertainty and the largest interest for neutron stars. The behaviour of the symmetry energy at supra-saturation densities can only be explored in terrestrial laboratories by using relativistic heavy-ion collisions of isospin asymmetric nuclei. Reaction simulations propose several potentially useful observable which should be sensitive to the behavior of the symmetry energy at suprasaturation densities, such as neutron and proton flows(direct and elliptic) [4,22,23], neutron/proton ratio [4,17,24, 25], / ratio and flows [4,22,26], 0 K / K [27] and / [26] ratios. To this day the problem is still open. Few works have provided constraints on symmetry energy behaviour at supra-saturation densities. The double ratio 41

42 0 0 ( K / K ) Ru /(K / K ) Zr was measured in 96 Ru + 96 Ru and 96 Zr + 96 Zr collisions at 1528 MeV/nucleon using the FOPI detector at GSI [28]; the experimental results show good agreement with the prediction of a thermal model in the case of the assumption of a soft symmetry energy for infinite nuclear matter. More realistic simulations in the frame of transport theory, for finite nuclear matter, show a similar good agreement with the data, but also exhibit a quite insensitivity to the symmetry term. However, it has recently been pointed out that more experimental and theoretical work are needed to establish the effectiveness of the K / 0 K ratio in probing the symmetry energy [4]. The single ratio / was measured in 197 Au Au [29] and analyzed using the hadronic transport model IBUU04 [30]. The results suggest that the symmetry energy is rather soft at supra-saturation densities; this finding, symmetry energy reaches its maximum at a density between ρ 0 and 2ρ 0 and then starts decreasing at higher densities, is not consistent with the density dependence deduced from fragmentation experiments probing nuclear matter near or below saturation density [17] and with the slightly softer density dependence resulting from the analysis of the pygmy dipole resonance in heavy nuclei [15]. Moreover, other theoretical works [31] suggest a reduced sensitivity of / ratio to the symmetry energy. Recently, the same set of FOPI data has been analyzed in the framework of the IMproved Isospin dependent Quantum Molecular Dynamics (Im- IQMD) [32]; it results a very stiff symmetry energy of the potential term proportional to u with the opposite of [30] results. 2, just Fig Asy-Stiff (F15) and Asy-Soft (F05) parameterizations of symmetry potential energy of nucleons as a function of the reduced nuclear density u, as used in UrQMD calculations; from ref. [36] It follows that also for the / ratio further work is needed to establish the effectiveness in probing the symmetry energy. In-medium absorption and reemission of pions can distort the asymptotic experimental signal and it is not clear which density of matter is explored by the pions signal. The analysis of another set of FOPI data is described in the third section of this paper. Neutron and proton elliptic flows One of the most promising probe of the symmetry energy strength at supra-saturation densities is the difference of the neutron and proton (or hydrogen) elliptic flows [33,34,35]. This has emerged mainly from calculations based on the Ultra-Relativistic Quantum Molecular Dynamics model (UrQMD) [37]. We report here some results obtained using UrQMD for the 197 Au+ 197 Au collision at 400 MeV/nucleon. The calculations have been performed using both Asy-Stiff ( 1.5 ) and Asy-Soft ( 0.5 ) potential symmetry energies, indicated as F15 and F05, respectively, in Fig. 1. A realistic description of the clustering processes during the evolution of the reaction is crucial for predicting dynamical properties of free neutrons, protons and light charged particles. In the UrQMD, the clustering algorithm is based on the evaluation of the proximity of nucleons in the phase space by using two parameters: the relative nucleon coordinates (Δr) and the relative momenta (Δp). The results presented here have been obtained using the cluster distributions built after a reaction time of 150 fm/c. The proximity parameters were: Δr=3.0 fm and Δp=275 MeV/c which are typical for QMD models [38]. As an example of the clusterization procedure, the charge distribution obtained for central collisions of Au+Au is shown in Fig. 2 in comparison with the data of Reisdorf et al. [39]. With a normalization at Z = 1, the overall dependence on Z is rather well reproduced but the yields of Z = 2 particles are under predicted by about a factor 3. The strong binding of 4 He particles is beyond the phase-space clustering criterion used in the model. However, also the 4π integrated yields of deuterons and tritons in central collisions are underestimated by similar factors of 2 to 3. The UrQMD predictions for the elliptic flow of neutrons, protons, and hydrogen as a function of rapidity in laboratory reference system Y lab for midperipheral collisions (impact parameter 5.5 < b < 7.5 fm) and for the two choices of the density dependence of the symmetry energy, are shown in Fig. 3. We remind here that direct v 1 and elliptic v 2 flows are obtained by the azimuthal particle distributions with the usual Fourier expansion: f ( ) 1 2 cos( ) 2 1 cos(2 1 (1) ) 42

43 Fig Fragment yields, integrated over the 4π solid angle, in central (equivalent to impact parameter b < 2:0 fm) collisions of 197 Au+ 197 Au at 400 MeV/nucleon as a function of Z (dots, from Ref. [29]) in comparison with UrQMD predictions normalized at Z=1 (histogram); adapted from Ref. [40]. with representing the azimuthal angle of the emitted particle with respect to the reaction plane [41]. The dominant difference is the significantly larger neutron squeeze-out in the Asy-Stiff case (upper panel) compared to the Asy-Soft case (lower panel). The proton and hydrogen flows respond only weakly, and in opposite direction, to the variation of within the interval of interest. Another interesting observable is the ratio of neutron and proton yields as a function of the transverse momentum pt (i.e. the component of momentum perpendicular to the beam direction). ASY-EOS experiment at GSI The experiment S394, "Constraining the Symmetry Energy at Supra- Saturation Densities With Measurements of Neutron and Proton Elliptic Flows", was devoted to measurements of neutron and proton elliptic flows in isospin asymmetric systems 197 Au Au, 96 Ru + 96 Ru and 96 Zr + 96 Zr at 400 MeV/nucleon. Simultaneous measurements of neutron-proton yield ratio, flow and isotopic ratio for light fragments was performed; all these measurements could allow to compare the symmetry energy as extracted by using several different nucleon-based observable. The Au+Au system is heavy and neutron-rich. Simulations with UrQMD predict large sensitivity of the symmetry energy on the neutron-proton observable for this system. Using Ru+Ru and Zr+Zr systems could allow us to compare neutron-rich and neutron-deficient systems; the 96 Ru and 96 Zr combination is unique among available stable isotopes in that it is mass symmetric and isobaric. The measurement with these systems are very important in order to reduce systematic errors. Besides, the collected data could provide important information to pin up effects related Fig Elliptic flow parameter for midperipheral (impact parameter 5.5 < b < 7.5fm) 197 Au Au collisions at 400 MeV/nucleon as calculated with the UrQMD model for neutrons (dots), protons (circles), and all hydrogen isotopes (Z=1, open triangles), integrated over transverse momentum pt, as a function of the laboratory rapidity Y lab. The predictions obtained with a stiff and a soft density dependence of the symmetry term are given in the upper and lower panels, respectively. The experimental result from Ref. [42] for Z = 1 particles at mid-rapidity is represented by the filled triangle (the horizontal bar represents the experimental rapidity interval); adapted from Ref. [40]. to the size, the total charge and the surface of the nuclear system. This experiment aims to achieve high quality of the analysis by increasing the statistics by factor expected to be around compared to the previous experiments. Fig Schematic view of experimental setup. 43

44 parallel to standard analogical one, has been of fundamental importance allowing us to store directly the shape the electronic signals; an off-line analysis is then useful in order to study the best processing system and to develop new electronic solutions. Conclusions Fig Fast vs Slow component scatter plot as obtained in a CHIMERA CsI(Tl) scintillator placed at a polar angle 9 lab for Au+Au reaction at 400 MeV/nucleon at GSI; lines of particles stopped and passing through CsI detector are indicated by arrows. During the experiment (see Fig. 4 for a schematic view) we used LAND [46], time-of-flight detector for high energetic neutrons and light charged particles in a similar geometry like in [43] to measure neutron squeeze-out. LAND has been positioned around 45, to cover the mid-rapidity for a large lab transverse momentum region. Protons can be separated by employing the calorimetric properties of the neutron detector and the measured proton observable can be compared directly to the FOPI data measured in a similar angular acceptance. The simultaneous measurement of the atomic number Z and the azimuthal angle for fragment emissions in the forward direction will be essential for a precise determination of the modulus and orientation (reaction plane) of the impact parameter; this task has been accomplished by using a detection system with high granularity at forward angles ( 7 lab 20 ) consisting of 8 CsI rings (352 modules) of the CHIMERA multi-detector [47] and the ALADIN Time-Of-Flight wall [48]. Preliminary results revealed a good charge identification performance for light charged particles using the fast-slow technique in the CsI detectors (Fig.5) and the capability of reconstructing the reaction plane. In addition, flow of light fragments have been measured with the Krakow telescope array positioned on the opposite side of LAND, at angles ( 21 lab 60 ). The use of digital acquisition techniques [49] in about 10 % of the detectors, in New experiments on symmetry energy at suprasaturation densities are expected to take place during the next few years, in Europe as well as worldwide. It is likely that providing definitive constraints on the symmetry energy will require simultaneous measurements of several observable. However, the isospin signals at supra-saturation densities appear to be controversial and strongly model dependent; to clarify these points, we need a better understanding of volume, Coulomb and surface effects, production and reabsorption of resonances, reaction dynamics, inmedium nucleon-nucleon cross section, splitting of neutron and proton effective masses in momentum dependent iso-vectorial interactions. Neutron and proton elliptic flows appear to be as one of the most interesting observable with strong sensitivity to symmetry energy. The ASY-EOS experiment at GSI was performed properly to measure such and other isospin sensitive observable in reactions of isospin asymmetric systems at pre-relativistic energies, in order to provide quantitative information on the density dependence of symmetry energy at supra-normal saturation density. The author would like to thank the people that made this work possible: the whole INFN-CHIMERA- EXOCHIM collaboration in Catania, Messina, Naples and Milano, the GSI-Group and the ASY-EOS collaboration for their support and exceptional work. References [1] Fuchs C. and Wolter H.H., Eur. Phys. J. A, 30 (2006) 5; [2] KlÄahn T. et al., Phys. Rev. C, 74 (2006) ; [3] Baran V. et al., Phys. Rep., 410 (2005) 335; [4] Li B.-A. et al., Phys. Rep., 464 (2008) 113; [5] Lattimer J.M. and Prakash M., Science, 304 (2004) 536; [6] Danielewicz P. et al., Science, 298 (2002) 1592; [7] Youngblood D.H. et al, Phys. Rev. Lett., 82 (1999) 691; [8] Lattimer J.M. and Prakash M., Phys. Rep., 333 (2000) 121; [9] Botvina A.S. and Mishustin I.N., Phys. Lett. B, 584 (2004) 233; [10] Horowitz C.J. and Piekarewicz J., Phys. Rev. Lett., 86 (2001) 5647; [11] Wiringa R.B. and Pieper S.C., Phys. Rev. Lett., 89 (2002) ; [12] Chang Xu and Li B.-A., Phys. Rev. C, 81 (2010) ; [13] Li T. et al., Phys. Rev. Lett., 99 (2007) ; [14] Trippa L. et al., Phys. Rev. C, 77 (2008) ; [15] Klimkiewicz A. et al., Phys. Rev. C, 76 (2007) ; [16] Tsang M.B. et al., Phys. Rev. Lett., 92 (2004) ; [17] Tsang M.B. et al., Phys. Rev. Lett., 102 (2009) ; [18] Famiano M. et al., Phys. Rev. Lett., 97 (2009) ; [19] Iglio J. et al., Phys. Rev. C, 74 (2006) ; 44

45 [20] Tsang M.B. et al., Phys. Rev. Lett., 86 (2001) 5023; [21] Amorini F. et al., Phys. Rev. Lett, 102 (2009) ; [22] Yong G.-C. et al., Phys. Rev. C, 74 (2006) ; Yong G.-C. et al., Phys. Rev. C, 73; [23] Greco V. et al., Phys. Lett. B, 562 (2003) 215; [24] Li B.-A. et al., Phys. Lett. B, 634 (2006) 378; [25] Li Q. et al., Phys. Rev. C, 73 (2006) ; [26] Li Q. et al., Phys. Rev. C, 71 (2005) ; [27] Ferini G. et al., Phys. Rev. Lett., 97 (2006) ; [28] Lopez X. et al., Phys. Rev. C, 75 (2007) ; [29] Reisdorf W. et al., Nucl. Phys. A, 781 (2007) 459; [30] Xiao Z. et al., Phys. Rev. Lett., 102 (2009) ; [31] Li Q. et al., J. Phys. G, 32 (2006) 407; [32] Zhao-Qing Feng, Gen-Ming Jin,, Phys. Lett. B, 683 (2010) 140; [33] Trautmann W. et al., arxiv: , (2009); [34] Trautmann W. et al.,, Prog. Part. Nucl. Phys., 62 (2009) 425; [35] Trautmann W. et al.,, Int. J. Mod. Phys.E, 19 (2010) 1653; [36] Li Q. et al., J. Phys. G, 31 (2005) 1359; [37] see UrQmd homepage, [38] Yingxun Zhang and Zhuxia Li,, Phys. Rev. C, 74 (2006) ; [39] Reisdorf W. et al., Nucl. Phys. A, 612 (1997) 493; [40] Russotto P. et al., in Proceedings of the XLVI International Winter Meeting On Nuclear Physics, edited by Iori I. and Tarantola A. (Università degli Studi di Milano) 2008, pp ; [41] Andronic A. et al., Eur. Phys. J. A, 30 (2008) 31; [42] Andronic A. et al., Phys. Lett. B, 612 (2005) 173; [43] Leifels Y. et al., Phys. Rev. Lett., 71 (1993) 963; [44] Lambrecht D. et al., Z. Phys. A, 350 (1994) 115; [45] Li Q. et al., Mod. Phys. Lett. A, 9 (2010) 669; [46] Blaich Th. et al., Nucl. Instrum. Methods Phys. Res. A, 314 (1992); [47] Pagano A. et al., Nucl. Phys. A, 734 (2004) 504; [48] SchÄuttauf A. et al., Nucl. Phys. A, 607 (1996) 457; [49] Amorini F. et al., IEEE Trans. Nucl. Sci., 55 (2008) 717; 45

46 46

47 PREMIO APP PER UNA TESI DI DOTTORATO Paolo V. Giaquinta Università degli Studi di Messina Quest anno è stata celebrata la prima edizione del premio conferito congiuntamente dall Accademia Peloritana dei Pericolanti (APP) - segnatamente, dalla Classe di Scienze Fisiche, Matematiche e Naturali della stessa Accademia - e dal Corso di Dottorato di Ricerca in Fisica all autore della tesi di dottorato, afferente al XXIII ciclo, distintasi particolarmente per originalità e contenuti. La valutazione delle tesi presentate dai candidati al premio è stata effettuata da una commissione insediata ad hoc dal Collegio dei Docenti del Corso di Dottorato; la commissione era presieduta dal Prof. Lorenzo Torrisi, Coordinatore del Corso di Dottorato, ed era composta dai Proff. Giuseppe Carini, Giorgio Giardina, Domenico Majolino e Paolo V. Giaquinta, quest ultimo anche nella qualità di Direttore della Classe di Scienze FF.MM.NN. dell Accademia Peloritana dei Pericolanti. La commissione, riunitasi il 20 aprile 2011, ha deliberato all unanimità di assegnare il premio al Dott. Alessandro Ridolfo per la tesi intitolata Quantum optical properties of strongly coupled systems, con la seguente motivazione: La tesi del Dr. Ridolfo, di cui si riporta in calce il sommario, riguarda una trattazione quantistica nel campo dell opto-elettronica. Nanoparticelle e nanostrutture sono capaci di focalizzare fotoni a dimensioni più piccole della lunghezza d onda. In tal modo è possibile aumentare la densità ottica degli stati anche in una microcavità. La tesi affronta lo studio teorico di questi sistemi quantici. Le indagini effettuate fanno prevedere la possibilità di migliorare in futuro dispositivi quanto-fotonici, basati su semiconduttori, di dimensione nanometrica che possono essere sensibili anche a fotoni singoli e che possono adoperarsi per emissioni di luce laser da dispositivi nanometrici. La trattazione approfondita del problema, l approccio quantistico adoperato, l originalità della tematica affrontata e le possibili ricadute applicative che i dispositivi a semiconduttore potrebbero avere, hanno contribuito a fare giudicare la tesi del Dr. Ridolfo di elevata qualità, originalità e approfondimento, ben meritevole dunque del premio in oggetto. L attestato di merito è stato consegnato dal Prof. Paolo V. Giaquinta al Dott. Alessandro Ridolfo in occasione della II Giornata di Studio del Dottorato di Ricerca in Fisica. Il premio conferito dà anche titolo alla pubblicazione di un ampio estratto della tesi sugli Atti della Accademia Peloritana dei Pericolanti (AAPP) - Classe di Scienze Fisiche, Matematiche e Naturali, una rivista scientifica multidisciplinare pubblicata in formato elettronico e liberamente accessibile sul dominio internet: Sommario della Tesi QUANTUM OPTICAL PROPERTIES OF STRONGLY COUPLED SYSTEMS The realization of solid state devices able to control the single photon states is of great importance in the field of Quantum Information and Opto-electronics. Re- cently, significant developments have been achieved by coupling single quantum emitters (QEs) in optical microcavities with high Q factor. The main limitation of these devices is represented by the size of the cavities that can not be smaller than half wavelength, and in practice are much larger because of the presence of mirrors or photonic crystals required to obtain the optical confinement. However, nanoparticles (NPs) and metallic nanostructures are able to focus the electromagnetic waves to spots much smaller than a wavelength. In this way, it is possible to increase the optical density of states, as well as with the microcavity, but with more compact structure. The ability of metal NPs to control the radiative decay of the QEs nearly positioned has been widely demonstrated both theoretically and experimentally. In this thesis I ve been studied, from the theoretical point of view, the optical proper- ties of these quantum systems, in various coupling regime. In the first part it was developed a theoretical framework based on the calculation of the Master Equation (ME), which has helped to investigate the photoluminescence s properties of micro- cavity coupled to QEs optically excited via incoherent pumping. In such systems, under low excitation density, it was possible to obtain analytical formulas that de- scribe the processes associated with the first-order correlations (photoluminescence spectra). The results obtained from the fit of the experimental data show an excel- lent agreement with our theoretical results. In particular, it has been shown highly predictive nature in the case of photonic polaritons in an organic double microcav- ity: the fit of the photoluminescence of one of the two microcavities has enabled the calculation of the photoluminescence of the whole structure (A. Ridolfo et al. Phys. Rev. B 81, (2010)). At high-density excitation, calculation s technique in non-perturbative regime (based on the truncation of the number of photons) has led to some important results in the study of nonlinear optical processes. Subse- quently, the ME formalism was extended to the case of structures made 47

48 of metal NPs coupled to QES that, because of their spectroscopic properties, are also called artificial hybrid molecules. The extension of the theoretical framework was made possible by modeling the appropriate electromagnetic field which arises from the presence of electronic excitations on the surface of metal NPs called plasmons. The results, which refer to the silver NPs, show that the inelastic part of the resonance fluorescence increases more than two orders of magnitude than the QE alone. It also reported a careful study of the statistical properties of the scattered light by calculating the second order correlation function, which is strongly influenced by the presence Fano effect, originating from the interaction between the QE discrete excitation and the continuous band of plasmon. The calculation of the scattering spectra and of the intensity correlations, shows that this system can be used as a single photon ultra-compact optical transistor: the scattering of a first photon of appropriate frequency, is able to activate (or inhibit) the scattering of a second photon (A. Ridolfo et al., Phys. Rev. Lett (in press)). In the next chapter, with ac- curate calculations of electromagnetic scattering based on the T-matrix, it has been demonstrated that it is possible to realize the strong coupling regime in the case of many QEs and single QE (S. Savasta et al., ACS Nano, 4, (2010)). In the first case, the cross section of extinction, calculated for a structure consisting of a silver nanoparticle coated with a dielectric matrix doped with photoluminescent molecules, has showed the characteristic anticrossing typical of the strong coupling regime. In the second case, replacing the single-nanoparticle geometry with the two-nanoparticle geometry in order to obtain an increase of the plasmonic field in the center of the principal axis to obtain the strong coupling regime with a single QE. Again, calculations have showed the achievement of the regime of strong inter- action in a structure whose maximum size is only 40 nm! From the results obtained thus good prospectives emerge for possible applications in Quantum Information or to create devices that can process individual photons. This will make it pos- sible to implement devices for Photonic Quantum Computation without renounce to the nanometric dimensions of the compact modern nano-sized semiconductor logical gates. In the secondlast chapter has been presented a theoretical analysis of all-optical control of the strong coupling regime (dynamic switching-on/off) be- tween a single QE and an optically confined microcavity-mode, by sending optical pulses control of appropriate area, able to determine transitions to and from the third lower level energy of the QE (A. Ridolfo et al., Phys. Rev. Lett (in press)). The chosen scheme describes the system recently used in experiments on adiabatic- switching for inter-sub-polaritons (Guenter G. et al. Nature 458, 178 (2009)), but it can also be applied to the study of optical transitions exciton-biexciton cascade or other transitions, in which are present the cavity polaritons. From our results, important conclusions are drawn about the possibilities and limitations of the im- portant experimental design proposed: once Rabi oscillations have been induced with a first control pulse, depending on the time of arrival of a second control pulse, Rabi oscillations can be suppressed or not, also influencing the coherence properties of the whole system. The theoretical results obtained are very fascinating and will stimulate the achievement of new experimental and technology goals. Finally, in the last chapter it has been studied the dynamic behavior of en- tanglement in a system consisting of two solid state QEs enclosed in two separate microcavities. In this solid state system, in addition to coupling with the cavity mode, the QE is coupled to a continuum of modes that provide a lossy channel to which is adds a further loss caused by the phases losses induced by interaction with thermal phonons. This configuration has been modeled as a multiparty system consisting of two independent subparts, each containing a single q-bit and a single cavity mode, subject to losses, radiative and non-radiative decay (pure-dephasing). The theoretical results obtained by the usual framework of ME already used in pre- vious chapters have highlighted the important destructive impact on the evolution of entanglementdynamics caused by pure-dephasing. The experimental informa- tion in these systems can be obtained from the detection of the light escaping from the cavity. With an appropriate choice of physical parameters of the model, corre- sponding to values that are extrapolated from the experiments, was simulated the dynamic evolution of entanglement in two realistic situations (K. Hennessy et al. Nature 445, 896 (2008) V. Loo V et al. arxiv: v1 [cond mat.mes-hall] (2010)). Thus, the work places emphasis on the negative impact of puredephasing, always present in solid state devices, on the entanglement decay. 48

49 PHD E MONDO DEL LAVORO: STATISTICHE SUL PLACEMENT POST DOTTORATO Paola Donato Dipartimento di Fisica, Università di Messina Dottorato di Ricerca in Fisica, Università di Messina 1. Introduzione È stato sfruttato il database del dottorato di ricerca in Fisica per condurre un indagine sul placement dei dottori di ricerca in Fisica dell Università degli Studi di Messina relativamente ai cicli dal XIII al XXIII. Occorre premettere che si è fatto in modo di curare e far crescere il database del dottorato, strumento indispensabile per questo tipo di analisi. Il database, infatti, è stato avviato sin dal primo ciclo di dottorato (1983) e, di anno in anno, aggiornato e integrato. Ritengo sia di importanza fondamentale curare e migliorare i dati in nostro possesso, poiché questi sono in grado di restituirci una visione globale del lavoro svolto dai docenti e dai dottorandi, oltre che una valutazione complessiva della funzione didatticoformativa del dottorato in vista della collocazione nel mondo della ricerca e del lavoro. Proprio di quest ultimo aspetto mi sono occupata in questa breve indagine. Altra importante premessa, inoltre, riguarda la scelta di collocare questa indagine all interno di un range temporale ristretto agli effettivi impieghi dichiarati da sessanta dottori di ricerca in Fisica, dottorati negli ultimi dieci anni (dal XIII al XXIII ciclo) presso il Nostro Ateneo. 2. Macro-aree di impiego lavorativo post-doc Per descrivere l andamento dell occupazione postdottorato si è ritenuto opportuno suddividere la collocazione dei dottori di ricerca in Fisica in quattro macroaree di impiego. Se da un lato, infatti, le macroaree risultavano facilmente individuabili i dati rilevati evidenziavano la presenza di queste quattro principali aree di impiego, dall altra parte si voleva tener conto di quegli sbocchi lavorativi meno presenti per locazione geografica e/o territoriale, in modo tale da rendere il futuro confronto con i dati statistici di altri atenei il più possibile coerente. Le aree scelte sono state quattro: Università: All interno di questa macroarea sono stati considerati i dottori di ricerca che a oggi ricoprono il ruolo di ricercatori di ruolo, ricercatori a tempo determinato, gli assegnisti di ricerca, i borsisti post-doc; Scuola: All interno di questa macroarea rientrano tutti quei dottori di ricerca che sono attualmente impiegati nella scuola secondaria superiore; Enti di ricerca e industrie: All interno di questa macroarea abbiamo considerato quei dottori di ricerca che sono occupati presso: INFN, CNR, ENEA, Fondazioni, ST- Microelectronics; Altro: All interno di questa macroarea abbiamo inserito tutte quelle attività lavorative che non rientrano nelle tre precedenti aree. 3. Densità dei cicli Un aspetto importante che si è deciso di prendere in considerazione prima di addentrarci nel dettaglio delle collocazioni lavorative dei dottori di ricerca, è stato quello della scelta del curriculum all interno del corso di dottorato. Il grafico (A) evidenzia che la principale scelta dei dottorandi riguarda il curriculum di Struttura della Materia, affiancato da quello di Fisica Nucleare e seguito a distanza dai curricula di più recente istituzione, cioè quelli di Fisica Applicata ai Beni Culturali, di Fisica Applicata ai Beni Ambientali e quello di Fisica della Materia Soffice e dei Sistemi Complessi. L interesse del dato, ovviamente, risiede nella sua successiva declinazione in funzione dell impiego lavorativo. Ci è sembrato interessante, in altre parole, rilevare come e in che misura la scelta del curriculum può condizionare la tipologia di impiego lavorativo post-doc. Occorre tenere presente che il dato analizzato, di per sé già interessante, risulterà più significativo quando disporremo di maggiori informazioni relative ai curricula di più recente istituzione. 49

50 Densità Activity Report 2011 Dottorato di Ricerca in Fisica, Università di Messina DENSITA DEI CICLI CICLO Struttura della Materia Fisica Nucleare Fisica della Materia Soffice e dei Sistemi Complessi Fisica Applicata ai Beni Culturali XIII 4 1 XIV 5 XV 4 XVI XVII 4 1 XVIII XIX 4 2 XX XXI 3 1 XXII XXIII Fisica Applicata Beni Ambientali Grafico A: Numero dei dottorandi di ricerca in Fisica divisi per curriculum dal ciclo XIII al ciclo XXIII ai 5 Struttura della Materia Fisica nucleare Fisica della Materia Soffice e Sist. C. Fisica Applicata ai Beni Culturali Fisica Applicata ai Beni Ambientali XIII XIV XV XVI XVII XVIII XIX XX XXI XXII XXIII Ciclo 4. Dottorandi divisi per curriculum scelto all interno del Corso di Dottorato di Ricerca e loro placement. Il rapporto tra la densità dei cicli e l impiego lavorativo post-dottorato ha consentito di individuare quanto la scelta del curriculum abbia influenzato lo sbocco lavorativo. Il numero dei dottori di ricerca che hanno scelto il curriculum Struttura della Materia e Fisica Nucleare maggiore perché questi curricula sono stati istituiti da maggior tempo rispetto agli altri è preponderante in tutti gli ambiti lavorativi. Desidero evidenziare che sono i soli presenti nell ambito universitario, probabilmente perché i relativi settori di applicazione, a livello sia nazionale sia internazionale, offrono maggiori opportunità di impiego. I dati sono indicativi anche per ciò che riguarda l impiego nel settore scolastico. Pur non essendo storicamente l insegnamento uno degli sbocchi naturali per i laureati in Fisica, nondimeno è possibile rilevare come il mondo scolastico rappresenti una risorsa lavorativa importante per coloro che conseguono un dottorato di ricerca. Il dato riportato nel grafico (B), più in particolare, ci restituisce una distribuzione nel settore scolastico pressoché equa tra tutti i curricula del dottorato. Importante sbocco lavorativo, inoltre, è quello degli enti di ricerca, quali, ad esempio, INFN, CNR, ST 50

51 Densità Activity Report 2011 Dottorato di Ricerca in Fisica, Università di Messina Microelectronics, Arpa. Non sono presenti in questa macroarea, come evidenzia il grafico B, dottori di ricerca in Fisica Applicata ai Beni Culturali e Beni Ambientali. Quasi sicuramente quest ultimo dato è legato ad una scelta di specializzazione che, già a monte, è orientata ad una implementazione maggiormente operativa delle conoscenze acquisite. Quasi tutti i curricula, infine, contribuiscono alla macroarea che abbiamo definito altro. Scuola Università Enti di Ricerca Altro Totale Struttura della Materia Fisica Nucleare Fisica della Materia Soffice e dei Sistemi / / Complessi Fisica Applicata ai Beni Culturali 3 / / / 3 Fisica Applicata ai Beni Ambientali 2 / / 1 3 Totale Grafico B: Dottorandi divisi per curricula scelto all interno del Corso di Dottorato di Ricerca e loro placement. 20 Struttura della Materia Fisica nucleare Fisica della Materia Soffice e Sist. C. Fisica Applicata ai Beni Culturali Fisica Applicata ai Beni Ambientali Scuola Università Enti di Ricerca Altro Occupazione 5. Densità occupazionale Considerando in modo più generalizzato il dato relativo all impiego dei dottori di ricerca, prescindendo cioè dal curriculum scelto, risulta una suddivisione nelle macroaree come riportato nel grafico (C). 51

52 D e n s ità Activity Report 2011 Dottorato di Ricerca in Fisica, Università di Messina DENSITA OCCUPAZIONALE CICLO SCUOLA UNIVERSITA ENTI DI ALTRO TOTALE RICERCA XIII XIV XV XVI XVII XVIII XIX XX XXI XXII XXIII TOTALE Grafico C: Numero dei dottori di ricerca in Fisica dal ciclo XIII al ciclo XXIII e loro placement S c u o la U n i v e r s it à E n ti d i R i c e r c a A l tr o O c c u p a z io n e Il ruolo principale nel placement dei dottori di ricerca viene svolto dall istituzione universitaria. Nel grafico (D) si è cercato di evidenziare il rapporto tra i dottori di ricerca che sono stati assorbiti dal mondo universitario in modo strutturale e quelli che non hanno ancora una collocazione stabile. Ci siamo soffermati su questo aspetto sia per sottolineare come, in modo analogo ad altri settori lavorativi della nostra società, anche nel mondo universitario il lavoro precario svolga una funzione preponderante rispetto a quello stabile, sia per confrontare il dato in nostro possesso con un altra importante realtà universitaria nazionale. 52

53 D ottorato in Fisica Di Messina Area occupazionale : Univers ità 7 3,3 3% Strutturati Estero Strutturati Italia Non Strutturati 1 6,6 7% 10% Grafico D Come si può rilevare dal grafico (E), infatti, il dato tendenziale risultante dai dati messi a disposizione dall Università degli Studi di Roma Tor Vergata dal XVIII al XXIII ciclo sono identici a quelli risultanti dagli undici cicli presi in considerazione nell ateneo messinese. Questo conferma che solo circa un quarto dei dottori di ricerca riesce a rimanere in modo permanente all interno del mondo universitario. Un altro dato rilevante, a nostro parere, è che circa un terzo degli strutturati viene assorbito dalle Università straniere. Questo dato è importante perché conferma la spendibilità all estero delle competenze acquisite nel nostro dottorato di ricerca, sebbene ci ricordi, nel contempo, che molte delle nostre migliori risorse non riescono a trovare spazio nel mondo del lavoro e della ricerca a livello nazionale. Area occupazionale U niversità To r V e rg a ta - R o m a 73,3 3 % S tru ttu ra ti Non Strutturati 2 6,67 % Grafico E 6. Placement dei dottori di ricerca: un confronto. Nell ultimo grafico sviluppato (F) abbiamo messo a confronto le tipologie occupazionali dei dottori di ricerca in Fisica dell ateneo messinese e di quello romano (Università Tor Vergata). Questo confronto è finalizzato innanzitutto a comprendere le diverse opportunità che il territorio offre a coloro che proseguono gli studi universitari conseguendo il titolo di dottore di ricerca. Ovviamente il dato si basa su indicazioni che non possono essere considerate esaustive, cosa che implicherebbe una ricerca a spettro molto più ampio rispetto a quello preso in considerazione in questa sede. Nondimeno, con il proposito di estendere ed approfondire in futuro i dati che ci saranno messi a disposizione da altri atenei italiani, riteniamo che questo grafico possa essere rappresentativo di una situazione di fatto comunemente nota. Il dato più evidente, in particolare, è il ruolo svolto dalla scuola nel placement post-dottorato nei due atenei. Se nella realtà messinese, infatti, più di un 53

54 dottore di ricerca su quattro trova impiego in ambito scolastico un dato, quest ultimo, che proietta la scuola al secondo posto tra le quattro macroaree prese in considerazione, nella realtà romana il placement nella scuola è quasi nullo, occupando, in percentuale, meno di tre dottori di ricerca su cento. Il dato non evidenzia maggiori opportunità di lavoro geograficamente localizzate nel comprensorio messinese-siciliano rispetto a quello romano, considerando che parte di coloro che si dedicano all insegnamento cercano e trovano la collocazione geografica della propria professione tanto a sud quanto al centro-nord d Italia. Questo significa, in altre parole, che l insegnamento, come sbocco di lavoro postdottorato, non è un dato fortemente condizionato dal territorio, se non per un retaggio culturale che richiederebbe, tuttavia, una analisi alquanto diversa da quella sviluppata in questa sede. Il secondo dato che emerge in modo evidente è che mentre l Università svolge un ruolo pressappoco uguale nella collocazione dei due atenei, diversa è la collocazione dei dottori di ricerca presso gli enti di ricerca. Benché, infatti, la macroarea dei dottori di ricerca messinesi che approdano agli enti di ricerca sia significativa il 15% è un dato sicuramente positivo non si può fare a meno di notare che il dato tendenziale relativo a questa macroarea nell ateneo romano sia di rilevanza assoluta, attestandosi intorno al 40%. Non v è dubbio che altre e più ampie riflessioni potrebbero essere sviluppate a partire dagli elementi in nostro possesso. Mi preme tuttavia sottolineare, in conclusione, che dati e analisi riportati in questa indagine vanno presi in considerazione in una prospettiva tendenziale e approssimativa, nel senso che quelli presentati in questa relazione sono soltanto i primi elementi di una ricerca che tende, per sua natura, ad un ampia raccolta di informazioni che verrà approfondita nel corso dei prossimi mesi. Pur essendo parziali, tuttavia, i dati a disposizione appaiono già significativi, a condizione, evidentemente, che vengano declinati in una chiave di lettura volta a comprendere la continua e rapida evoluzione del mondo del lavoro e la necessità che l istituzione universitaria riesca ad avere una sempre maggiore conoscenza e coscienza del placement di laureati e dottori di ricerca. Grafico F: Occupazione totale dei dottori di ricerca: un confronto Università degli Studi di Messina Università degli Studi di Roma Tor Vergata 40% 5 0% U nive rsità E nti 15 % Enti ricerca ri cer ca Al tr o Scu ola 8,33 % Università Altro Scuola 14,29% 2,86% 26,67 % 42,86% Bibliografia [1] Activity Report 2010, Dottorato di Ricerca in Fisica dell Università di Messina, L.Torrisi Ed. ISSN n , [2] Sito WEB Università degli Studi di Roma Tor Vergata: 54

55 AN OVERVIEW OF RESEARCH ACTIVITIES IN THE PHYSICS PHD COURSE F. Caridi a,b, L. Torrisi c,d a)facoltà di Scienze MM. FF. NN., Università di Messina, Viale F. Stagno d Alcontres, Messina, Italy. b)infn-sez. CT, Gr. Coll. di Messina, Viale F. Stagno d Alcontres, Messina, Italy. c)dipartimento di Fisica, Università di Messina, Viale F. Stagno d Alcontres, Messina, Italy. d)infn-lns, Via S. Sofia 44, 95124, Catania, Italy. Abstract An overview of research activities of the PhD course in Physics of the Messina University is reported. The research is developed mainly in the areas of matter structure, applied, theoretical and nuclear physics. Many different laboratories are available for PhD students: laboratory of plasma physics; laboratory of acoustic and dielectric spectroscopy; laboratory of spectroscopy, biophysics and applied physics; laboratory for studying nuclear reactions on nucleons and nuclei; laboratory of IR and Raman spectroscopy; nuclear physics laboratories; laboratory of low temperature physics; laboratory of computational physics; laboratory of microanalysis, spectroscopic techniques and nanomaterials; laboratory of optical spectroscopy and laboratory of spectroscopic analyses. A particular attention is given to collaborations of research groups and issues covered by PhD theses in recent years. Research laboratories The laboratories of the PhD course are reported in Table I. Laboratory Laboratory of plasma physics Laboratory of acoustic and dielectric spectroscopy Laboratory of spectroscopic techniques, biophysics and applied physics Laboratory for studying nuclear reactions on nucleons and nuclei IR and Raman Spectroscopy Laboratory Nuclear Physics Laboratories Laboratory of low temperature physics Responsible Prof. L. Torrisi Prof. M. Cutroni Prof. S. Magazù Prof. G. Giardina Prof. D. Majolino Prof. R.C. Barnà Prof. G. Carini Laboratory of computational physics Prof. C. Caccamo Introduction The Doctorate in Physics of the Messina University has the aim to provide a satisfactory degree of competence and professionalism in the field of Condensed matter, Nuclear Physics, Bio-Physics and cultural heritage and environmental Applied Physics. The research activities are developed mainly at the Physics Department and at the Matter Physics and Electronic Engineering Department of Messina University, at the National Institute of Nuclear Physics (INFN) and at the Institute for Chemical and Physical processes (IPCF) of Messina CNR. Many other national and international collaborations also give the possibility to improve the scientific knowledge of PhD students, working in big facilities of last generation. Laboratory of microanalysis, spectroscopic techniques and nanomaterials Laboratory of optical spectroscopy Laboratory of spectroscopic analyses Prof. F. Neri Prof. G. Mondio Prof. L. Silipigni Tab. I: Research laboratories of the PhD course LABORATORY OF PLASMA PHYSICS Instrumentation: Laser Nd:YAG, 1064 nm e 532 nm, 3 ns, mj, mass quadrupole spectrometer with energy filter HIDEN EQP 300, classic mass quadrupole spectrometer BALZERS PRISMA 300, Langmuir probe, optical spectroscope, Faraday cup for time-of-flight measurements, optics and vacuum systems, detection electronics (Fig. 1). Research activity: the experimental setup consists in a Nd:Yag laser, operating at 1064 and 532 nm, with a pulse width of 3 ns and maximum energy of 300 mj. The beam is focalized through a optical lens at a distance of 50 cm, in order to have, in the solid target, inside a vacuum chamber, a laser spot of around 1 mm 2 55

56 at pressure of the order of 10-6 mbar. The interaction of the beam with the target produces an ablation and consequently plasma generation [1]. Applications: diagnostic of plasma laser-generated, deposition of thin films (Pulsed Laser Deposition), laser welding, nuclear physics (Laser Ion Source, D-D fusion), cultural heritage applications (compounds, isotopic ratios, surface patina analysis). IC Vacuum chamber Laser MQS Fig. 1: Experimental setup of the Laboratory of Plasma Physics of Messina. Collaborations: INFN-LNS, ASCR PALS Lab., Institute of Plasma Physics and Laser Microfusion, University of Pisa, Salento, Roma Tor Vergata and Milano-Bicocca, CELIA (Centre Lasers Intenses et Applications), MT-LAB, Bruno Kessler foundation. LABORATORY OF ACOUSTIC AND DIELECTRIC SPECTROSCOPY Instrumentation: setup for ultrasound analysis (MATEC TB1000 e MATEC 6000), setup for wide band measurements, wave guides. Research activity: condensed states physics. It principally concerns problems of disorderly systems behavior. Different techniques, structural and dynamics, are employed: ultrasound (khz-mhz), fully employed in physics and engineering for nondestroying tests (NDT), dielectric spectroscopy (systems for wide band measurements 10-3 Hz - 2 GHz), to measure the real part ε '(ω), and the imaginary part ε (ω), of the complex permittivity of a material (solid, liquid) in a wide range of frequency 10-3 Hz-2 GHz, at temperatures between 450 K and 3 K using only one sample. Wave guides (8.2 GHz 40 GHz) are also employed for measurements of the complex permittivity at a frequency in the microwave range with transmission lines at rectangular wave guides and at temperatures between the room value and 10 K [2]. Collaborations: University of Pavia, CNR ITC, Arizona State University, Texas Tech University, Universidad Autonoma de Madrid, Chalmers University of Technology. LABORATORY OF SPECTROSCOPIC TECHNIQUES, BIOPHYSICS AND APPLIED PHYSICS Instrumentation: experimental setup for static and quasi-elastic scattering measurements, infrared spectrometer for biophysics measurements. Research activity: the laboratory disposes of toptable devices (spectroscopic techniques of elastic type, quasi-elastic and inelastic of electromagnetic radiation) useful to the dimensional and morphologic, qualitative, structural, dynamic and thermodynamic characterization of a wide class of materials of physical, biotechnological and industrial interest. The laboratory also disposes of instrumentation for measurements and analysis for ambient studies (electromagnetic pollution, air pollution, ) [3]. Applications: investigations about the mechanisms of bio-protection, micro-emulsion, gel micro-emulsion, innovative materials, physical and chemical properties of macro-molecular and polymeric systems of biological interest and optimization of physical devices for energetic and industrial fields. Collaborations: LDSMM (CNRS), CEMHTI (CNRS), Institute Laue Langevin, Rutherford Appleton Laboratory, BENSC, ESRF, Soleil, Sanofi-Aventis, Dompè, Labplants, Cosmetic Valley, ESA, Cape Town University. LABORATORY FOR STUDYING NUCLEAR REACTIONS ON NUCLEONS AND NUCLEI Research activity: study of barionic resonances by mesons photoproduction at the facility ELSA in Bonn (Germany) within the international cooperation BGOOD. The Messina group in BGOOD has the tasks of experimental setup simulations (activity carried out in site) and of hardware and software administration of hydrogen and deuterium cryogenic liquid target (activity carried out in site and at ELSA). Study of reactions induced by heavy ions for the production of superheavy elements. The experimental activity is carried out at China Institute of Atomic Energy (CIAE) in Beijing (China). Activity of calculation, experimental data analysis and interpretation is carried out in site. Study of Bremssthralung radiation emitted during spontaneous fission processes and alpha decay of heavy elements [4]. Collaborations: Institute for Nuclear Studies, Division of Nuclear and Particle Physics, Helmholtz- Institut fuer Strahlen und Kernphysik, Institut fuer Kernphysik, Institut fur Experimentelle Kernphysik, Institute for Theoretical and Experimental Physics, Institute of Physics Jagiellonian University, Ivane Javakhishvili State University of Tbilisi, Joint Institute for Nuclear Research, National Central University Jhongli, University of Bonn, Physikalisches Institut University of Bonn, 56

57 Helmholtz Institut f ur Strahlen- und Kernphysik, Petersburg Nuclear Physics Instute, University Roma Tor Vergata and INFN Roma2, INFN Roma1, INFN Laboratori Nazionali di Frascati, University of Pavia and INFN Pavia, University of Edinburgh, University of Kharkov, University of Moscow, Bogoliubov Laboratory for Theoretical Physics of JINR, Flerov Laboratory for Nuclear Reaction of JINR, Institute for Nuclear Research of NASU, Lomonosov Moscow State University. of the gas diffusion in irradiated Black PE, filament winding, dejection of mycotoxins of food flour, substances released during the irradiation of different types of PE, radiative treatment of adhesive joints for structural-type applications in the aerospace and automobile field, recognizing of materials by non destructive testing techniques, calibrations to recognize irradiated foods, development of new dosimeters for radiation processing and project of accelerating systems for industries interested [6]. IR AND RAMAN SPECTROSCOPY LABORATORY Instrumentation: Interferometry Spectrometer BOMEM DA8 for IR absorption measurements in Fourier Transform (FT-IR), for measurements in Attenuate Total Reflectivity (ATR), for FT-IR microspectroscopy and Raman scattering measurements in Fourier Transform. Pulverizer, hydraulic press, digital balance and electric stirrer with temperature control (50 C 350 C) to prepare and store samples. Portable XRF Analyzer Alpha 4000 Innov- Xsystems for X-Ray Fluorescence measurements (XRF). Research activity: complete characterization of dynamic and structural and/or compositional properties of matter, both in liquid state and solid state by the use of complementary spectroscopic tecniques. Thanks to the not invasivity of the techniques, these spectroscopic methodology can surely find a large and natural application in a lot of fields nowadays fundamental [5]. Applications: archeometry, characterization, storage and recover of cultural heritage, biomedicine and/or biophysics. Collaborations: BENSC (BErlin Neutron Scattering Center), ESRF (European Synchrotron Radiation Facility), ILL (Institut Laue-Langevin Facility), ISIS Rutherford-Appleton Laboratory Oxford, LLB (Laboratoire Lèon Brillouin). Nuclear physics laboratories RADIATION PROCESSING LABORATORY Instrumentation: Linac of electrons of 5 MeV (nominal energy 5 MeV, peak current ma, pulse time 3 sec, peak power 1 MW, power 1 kw, repetition frequency 1-300Hz, frequency RF GHz, No. accelerating cavities 9, no magnetic lens, beam diameter 4 mm). Applications: creation of new hydrogels, improvement of mechanic properties of UHMWPE and wood properties by impregnation and irradiation, study INFORMATICS LABORATORY Instrumentation: cluster of parallel computation (6 double-processors + file server). Protocols of Parallel Computation: PVM (Parallel Virtual Machine), MPI (Message Passing Interface). Research activity: Monte Carlo Simulation of radiation processing treatments by MCNP-4C2 code (Monte Carlo N Particle, version 4C2) and data analysis relative to experiments carried out with the CHIMERA multidetector (LNS). APPLIED NUCLEAR PHYSICS LABORATORY Instrumentation: lecture systems for optical dosimeters (Gafchromic) and rivelation system of cooling Ge(Li) + spectrometer α. Research activity: dose and dose-rate measurements, environmental radioactivity measurements (Radon measurements on samples of aspirated air on porous filters, radioactivity measurements in drinking water and on building materials). Collaborations: INFN, Institute for Physics and Nuclear Engineering, Institute of Physics, University of Silesia, Institute of Physics, Jagellonian University, Institute de Physique Nucleaire, IN2P3-CNRS and Université Paris-Sud Orsay, LPC, ENSI Caen and Université de Caen, Saha Institute of Nuclear Physics, Kolkata, GANIL, CEA, IN2P3-CNRS Caen, Institute of Nuclear Physics Cracow, Institute of Modern Physics Lanzhou, Institute of Experimental Physics Warsaw University. LABORATORY OF LOW TEMPERATURE PHYSICS Experimental techniques: mechanical spectroscopy and ultrasounds; low and high temperature calorimetry; Brillouin and Raman spectroscopy; low temperature techniques; high magnetic fields; preparation of glasses and polymers. Topics: influence of the disordered topology on the physical properties of materials; glass transition; low energy excitations; vibrational and relaxation dynamics. 57

58 Research activity: solid state physics. Materials: glasses and polymers [7]. Collaborations: Institut für Festkörperforschung, Forschungszentrum Jülich, IPCF-CNR Messina, Institute of Macromolecular Chemistry, National Academy of Sciences of Ukraine, IMEM-CNR Parma, Institute Laue-Langevin Grenoble, Department of Chemistry and Department of Physics and Astronomy, University of Tennessee. LABORATORY OF COMPUTATIONAL PHYSICS Instrumentation: Parallel Cluster made of 10 PC Pentium R Dual Core 2.60GHz 10Gb RAM, 4Tb, at the Department of Physics; parallel cluster made of 20 knots equipped with 4 Dual Core AMD Opteron Processor 280 and 4Gb RAM for each one (ex TriGRID project), allocated at the Center for Electronic Computing A. Villari ; access to grid managed by the Consorzio Cometa ( among the project PI2S2 ( Research activity: Statistical mechanical study of microscopic properties, structural and thermodynamic properties (including the phase equilibria) of simple and complex fluids. Integral theory of a fluid state for single site or several sites of interaction (Ornstein- Zernike equation, RISM Theory - Reference Interaction Site Model). Monte Carlo simulation methods and dynamic molecular models applied to both monatomic and molecular fluids, either pure or mixed. Collaborations: Laboratoire de Physique des Milieux Denses, Université de Metz, France, School of Physics University of Kwazulu-Nathal, Pietermaritzburg, South Africa, CNR-IPCF Messina, University La Sapienza Rome. Laboratory of microanalysis, spectroscopic techniques and nanomaterials LABORATORY OF MICROANALYSIS Instrumentation: microanalysis, imaging and depth profiling using XPS, high yield (tens of analysis/day), visual control of positioning for the microanalysis, argon ion gun for removing surface layers, electron gun to reduce the effects of electrical charging of insulating materials, software and libraries for the automatic recognition of the chemical composition. Automated setup for measuring dc electrical conductivity as a function of temperature ( K) using the volt-amperometric method for voltage or constant current. The system is equipped with a cryostat cooled with liquid nitrogen with optical windows, to measure photoconductivity. Measurements of profilometry and roughness on surfaces by scanning with lateral resolution of about 10 microns, and vertically up to 10 Å (Profilometer KLA- Tencor Alpha Step 500). Research activity: physical-chemical diagnostics, morphological, structural and electrical engineering, micro- and nano-scale solid surfaces and thin film multilayer structures. By means of X-ray photoemission spectroscopy (XPS), the surface compositional mapping on the micrometer scale and the effects due to the overlapping layers of different materials are analyzed, through the depth profile analysis. The study of compositional and structural properties of thin films of SRO (Silicon Rich Oxide) and silicon oxy-nitride devices for applications in power MOSFETs and thin-film photovoltaic converters was recently approached [8]. Collaborations: ANM Research, C.S.R.A.F.A, Messina. LABORATORY OF SPECTROSCOPIC TECHNIQUES Instrumentation: Raman spectroscopy system. Back-scattering configuration, laser sources: multi-line Argon, diode pumped Nd:YAG (second harmonic), He-Ne. Analyzer: flat field Triax 320 monochromator coupled with a BX 40 Olympus microscope and equipped with gratings of 1800 and 600 lines / mm holographic filter to eliminate the elastic scattering component. Detector: Diode matrix CCD , cooled with liquid nitrogen. Mapping micrometer with lateral resolution 1X1 (2 μm) using automated XY translation. Setup for measurements on colloidal solutions using a 10X lens focal length. Non-linear optical spectroscopy (Z-scan technique). Measurement system in the open and closed configuration of a pulsed laser beam transmission (Nd:YAG, 5 nsec), focused by a radiometric system with two sensors and the scanning engine of the sample along the optical axis. Research activity: physical-chemical characterization of bonding structures of materials in the form of thin films and colloidal solutions of nanoparticles: thin films of SRO (Silicon Rich Oxide), silicon-carbon alloys and carbon-based nanostructured systems, colloidal solutions of nanoparticles of metallic oxides and metallic nanoparticles for applications SERS (Surface Enhanced Raman Spectroscopy). Analysis of nonlinear optical response of colloidal systems of nanoparticles-based carbon and silicon: study of the absorption coefficient and refractive index as a function of laser pulse repetition rate, concentration and solvent. Collaborations: ANM Research, C.S.R.A.F.A, Messina. Laboratory of nanomaterials 58

59 Instrumentation: Nd-YAG laser pulse until the fourth harmonic (266 nm), power adjustable up to 180 mj (second harmonic), pulse duration 5 ns, repetition up to 20 Hz, optical beam focusing, handling and control of the metal target submerged in liquid (system for laser ablation in liquids). System for spraying deposition of thin layers of colloidal solutions: the technique of spraying by automated airbrush is a methodology used for the transfer of nanoparticles in colloidal phase on surfaces of various kinds (even flexible). The system consists of a compressed gas atomizer with interchangeable nozzles of various sizes. The nozzle is placed on a medium which ensures a movement for a uniform distribution of nanoparticles on the surface to be coated. The jet is directed into a deposition chamber that houses a sample holder heated to a temperature higher than the evaporation of the solvent. A system for the removal of moisture in the deposition chamber is also provided. Research activity: synthesis, laser ablation in liquids, and characterization of nanostructured metal oxides for the production of gas sensors and applications of metal nanoparticles for SERS (Surface Enhanced Raman Spectroscopy). Collaborations: ANM Research, C.S.R.A.F.A, Messina. LABORATORY OF OPTICAL SPECTROSCOPY Instrumentation: PE 750 UV-Vis-Nir Perkin Elmer ( nm), Lambda 2 UV-VIS-Nir Perkin-Elmer ( nm), FT-IR (Spectrum 100) Perkin Elmer ( cm -1 ) spectrophotometers; FluoroMax 2 Jobin Ivon ( nm) spectrophotofluorimeter; optical microscope. Research activity: optical spectrophotometry (UV- VIS-NIR). Measurements of absorption of electromagnetic radiation in the UV-VIS range allow to make a qualitative analysis of a given material. The profile of an absorption spectrum depends on various parameters such as the chemical and aggregation state of the analyzed sample. In addition, the absorption at a given wavelength depends on the nature and concentration of the analyte [9]. Collaborations: ST Microelectronics, Catania, CNR Messina, RIS Messina. LABORATORY OF SPECTROSCOPIC ANALYSES Instrumentation: System for dielectric and electrical transport measurements (RLC HP4284A shunt, RMC LTS-LN2-VT cryostat, vacuum system (~ 10-6 torr), temperature control device Lake Shore 330, Keithley 236 unit, pc). Research activity: study of electrical transport and dielectric properties of organic-inorganic hybrid multifunctional materials films and powders consisting of intercalation (nanocomposite) prepared by our research group. The electronic properties of these materials are also studied, using the photoelectronic spectrometer, dual anode Mg/Al K and the optical properties by means of spectrophotometers available in the laboratory of optical spectroscopy [10]. Collaborations: IPCF-CNR Messina, CNR Napoli. Conclusions During the last five years a number of twenty PhD in physics were formed at the Messina University. The experience accumulated during the years of doctoral and skills acquired allow them to aspire to scientific careers in universities, institutes of higher education, in research institutions and national (CNR, INFN, ENEA, ENI, etc..) and International Laboratories, with a special screening in Europe. The professionalism of a PhD doctor allows also the inclusion in any facility operating in areas requiring advanced professional skills through computer programming and simulation models of complex processes and teaching in secondary schools of physics, mathematics, electronic and information technology. References [1] L. Torrisi, F. Caridi, L. Giuffrida, Nucl. Instr. And Meth. B, 268 (2010) ; [2] A. Mandanici; M. Cutroni, R. Rickert, Journal of Non-Crystalline Solids, 357 (2) (2011); [3] S. Magazù, F. Migliardo, A. Benedetto, The Journal of Physical Chemistry B, 115 (24) (2011); [4] A.K. Nasirov, G. Mandaglio, M. Manganaro, A.I. Muminov, G. Fazio, G. Giardina, Physics Letters B, 686 (1) (2010); [5] G. Barone, V. Crupi, F. Longo, D. Majolino, P. Mazzoleni, V. Venuti, Journal of Molecular Structure, 993 (1-3) (2011); [6] Auditore L., Barna R.C., Emanuele U., Loria D., Trifiro A., Trimarchi M., Nucl. Instr. and Meth. B, 266 (10) (2008); [7] G. Carini, G. Tripodo, L. Borjesson, Materials Science & Engineering A, (2009); [8] E. Fazio, F. Neri, S. Patanè, L. D Urso, G. Compagnini, Carbon, 49 (1) (2011); [9] A.M. Mezzasalma, G. Mondio, T. Serafino, F. Caridi, L. Torrisi, Appl. Surf. Sci., 255 (7) (2009); [10] L. Silipigni, L. Schirò, L. Monsù Scolaro, G. De Luca, G. Salvato, Appl. Surf. Sci., 257 (24) (2011). 59

60 60

61 ENHANCED OPTICAL FIELDS FOR AGGREGATION OF METAL NANOANTENNAS AND LABEL FREE HIGHLY SENSITIVE DETECTION OF BIOMOLECULES B. Fazio a, *, C. D Andrea a,b, V. Villari a, N. Micali a, O. Maragò a, G. Calogero a and P.G. Gucciardi a a) CNR Istituto Processi Chimico-Fisici, viale F. Stagno D Alcontres 37, Messina, Italy * Corresponding author, fazio@me.cnr.it b)dottorato in Fisica dell Università di Messina, Dip.to di Fisica della Materia e Ingegneria Elettronica, viale F. Stagno D Alcontres, S. Agata-Messina, Italy Abstract Aggregated metal nanostructures are characterized by strongly intense electromagnetic fields localized in the cavities region, referred as hot spots, allowing for high sensitive vibrational spectroscopy. We report on the implementation of a laser induced Surface- Enhanced Raman Scattering sensor in liquid environment by controlled aggregation of gold nanorods dispersed in solution obtained through an interplay between thermal and radiation pressure effects. The creation of highly efficient hot spot regions enables the Raman detection of proteins dissolved in buffer solution at low concentration (down to 10-7 M) with an estimated enhancement factor of This methodology paves the way to a new generation lab-on-chip sensors that implies userfriendly experimental set up allowing for highly sensitive vibrational spectroscopy of biomolecules in their natural habitat and getting over the drawback of the standard methods based on the difficulty to manipulate metal nanostructures or realize active substrates that experience a highly efficient SERS. Introduction The discovery of Surface-Enhanced Raman Scattering (SERS) phenomena and single molecule sensitivity [1-5], due to the unique electronic and optical properties of metal nanoparticles, opened the doors to promising applications in material science and optical biosensors. SERS from isolated metal nanostructures is usually much weaker compared to what is observed on aggregates due to the strong field enhancement occurring in the gap regions (hot spots) between adjacent nanoobjects [2-5]. A controlled creation of hot spots in liquid, the natural habitat of biomolecules, is a challenge in which optical forces play an important role. Optical trapping (OT), manipulation and deposition of metal nanostructures, gold and silver, has been at the center of an intense research [6-9]. Here we show how the simultaneous occurrence of optical, mechanical and thermal effects, promotes aggregation of already formed gold nanorods staying in a colloidal suspension with the consequent creation of hot spot regions where biomolecules experience high field enhancement fundamental for their label free detection at submicromolar concentration. We validate the SERS biosensor efficiency by detecting biomolecules as Bovine Serum Albumin (BSA), Phenylalanine (Phe), Lysozyme (Lyz) and a protein not yet well known from a spectroscopical point of view, but of a great biomedical interest, the Manganese Superoxide Dismutase (MnSOD). Indeed, the MnSOD is considered a valid pathological biomarker, due to its levels in the plasma that are significantly higher in patients with ovarian carcinoma. Materials and methods Materials. Commercial gold nanorods (35x90 nm) are purchased from Nanopartz. They come in a DI water at a concentration of 0.05 mg/ml; the solution contains <0.1% ascorbic acid and <0.1% Cetyltrimethylammonium bromide (CTAB) surfactant capping preventing spontaneous re-aggregation, and have a positive -potential (+40 mv). The Bovine Serum Albumin buffered solutions at various concentrations (in the range between 10-3 M and 10-7 M) are prepared by mixing the suitable amount of BSA lyophilized powder (Sigma-Aldrich) with a 200 mm of Phosphate Buffer Solution (ph 7.2) obtained with Na 2 HPO 4 (14.94 g) and NaH 2 PO 4 (5,063 g) dissolved in 200mL of DIwater. Then, the gold nanorods solution is added to the prepared mixture with a ratio of 1:7 v/v. An amount of 75 l of BSA and NRs solution was put inside a typical glass cell used for optical trapping experiments. Following the same procedures we prepared analogous solutions containing gold nanorods and, respectively, Lyz at 10-6 M, MnSOD at 10-4 M and Phe at 10-3 M in PBS. Setup. We performed the SERS experiment using a Raman Micro-Spectrometer (LabRam HR800 - Horiba Jobin Yvon) coupled to the nm line of a He-Ne laser; the beam (P = 6.3 mw) was focused on a 500 nm diameter spot in the liquid, close to the bottom of the 61

62 cell, by a 100X microscope objective (Olympus, NA=0.95) a droplet of the BSA and NRs solution is put inside a glass cell (a model typically used for optical trapping experiments) and placed under a Raman Micro-Spectrometer (LabRam HR800 - Horiba Jobin Yvon) coupled to the nm line of a He-Ne laser. The spectrometer was equipped with a Peltier cooled CCD array (HJY-Synapse) as detector. The instrument was also employed to collect the extinction spectrum of the aggregate of gold NRs, by using a Xe lamp as white light source. the cell surface they aggregate for photoinduced thermal effect [9,10]. The extinction spectrum of the formed aggregate (figure 1,b), captured in situ, shows a broad band extinction feature, ranging between 420 and 900 nm and peaked at 770 nm, that dominates; it is suitable to underline that the nm of laser source, used as SERS probe, falls whithin the localized surface plasmon resonance of the aggregate, while it falls outside of the single rods plasmonic absorption features (figure 1,b blue line) at λ LSP = 687 nm and λ LSP = 527 nm, along their long and short axes respectively [11]. The relatively high energy density (~ 25 mw/µm 2 ) in the focal spot and the quasi resonant laser excitation of the LSPs modes causes a not negligible light absorption by the NPs which is partially converted into heat. By Stokes/Anti-Stokes Raman measurements we have estimated a temperature of about 60 C in the irradiated zone after 10 minutes of laser focusing. At this temperatures thermally induced structural rearrangement of gold nanorods in micelles capping has been observed [12]. Depolarized Light Scattering (DLS) measurements, here not shown, confirm that a thermal re-organization of the rods into small clusters takes place in the investigated solution at temperature as low as 60 C. Indeed, the mean hydrodynamic radius of about 65 nm, detected at room temperature and due to gold rods with a shell of BSA, likely stabilized by electrostatic interaction between the positively charged capping agent of the rods and the negative charge of BSA, becomes 100 nm for the gold/bsa aggregates at 60 C. Figure 1: (a) Sketch of the experiment and of the formed aggregate. (b) Absorption spectrum of the gold nanorods solution (blue line) compared to the extinction spectrum of the photo-induced aggregate (brown line). Results and discussion By manually changing the fine focus inside the solution and setting it at the bottom of the cell close to the rim, the intercepted gold nanorods are mechanically constrained in a confined region; the aggregation process is activated in some seconds; in figure 1.a a sketch of the experimental configuration and the aggregate formation. Due to the slightly blue shifted excitation with respect to their LSP resonance, the gold nanorods are subjected to both a scattering force and a repulsive gradient force, so that they are not trapped in the laser focus but rather strongly pushed towards the bottom of the sample cell along the optical axis. On Figure 2: (a) SERS of buffered BSA molecules at 0.1 mm (black line), 1 M (red line) and 0.1 M (blue line). (b) Raman spectrum of buffered BSA solution at 0.1 mm without nanorods induced aggregation. This increment of the mean size is due to thermal aggregation between gold rods mediated by BSA, that at this temperature is known to form small oligomers. 62

63 In figure 2 is shown the strong SERS signal of BSA molecules staying in the aggregates proximity, compared to the Raman signal of the same solution in absence of aggregates formation. We estimated a SERS enhancement factor of 2x10 5 by the ratio between the intensity of the SERS feature of the phenylalanine ring breathing at 1004 cm -1 obtained for the buffered solution of BSA at concentration of 10-7 M and the same Raman feature collected for a buffered solution of BSA 10-3 M without gold nanorods addition. BSA at 10-3 M corresponds to the concentration limit for the Raman detection in our experiment. Under the same experimental conditions (time=10s, 4 accumulations, after a NRs aggregation time of 30s) the intensities of the SERS spectra are not depending on the BSA concentration. This occurrence confirms that what we reveal is SERS from hot spot region and suggests us that tenths of micromolar concentration of protein is not a detection limit for our experiment. However, when a concentration of 10-8 M of BSA in PBS solution is added to the same concentration of NRs solution previously used, not stable aggregates are formed and we hardly collect only SERS spectra of the CTAB surfactant. In this latter case any BSA mediation and stabilization process occurs for aggregates formation, owing to the protein negligible amount that don t saturate the rods quantity; as a consequence, only a transient NRs aggregation due to the optical forces is experienced and immediately disrupted by the repulsive electrostatic action of the surfactant layer. The temporal dynamics of the photothermal creation of the hot spots can be followed by acquiring consecutive SERS spectra (figure 3a) and monitoring the temporal increase of the intensity of the protein spectral signatures. We observe a preferential increment of the features attributed to the aromatic residues in the structure (Phe, Tyr, Trp), due to the intercalation of the hydrophobic side chain into the CTAB layer. The high enhancement of the 1395cm -1 COO - symmetric stretching is due to the strong electrostatic interaction with the surfactant bilayer. A similar behavior has been observed by Kaminska and coworker in the interaction between bovine pancreatic trypsin inhibitor (BPTI) and CTAB-protected gold nanoparticles deposited on functionalized silicon surface [13,14]. Figure 3: Consecutive SERS spectra of BSA in PBS solution and gold nanorods (a). Trend vs time of some protein spectral features (b). The functionality of the SERS biosensor obtained by photoinduced aggregation of gold nanorods has been validated for many molecules of biological interest. In figure 4.a,b,c the SERS spectra of lysozyme protein, Phenylalanine amminoacid and Manganese Superoxide Dismutase, compared to the Raman signal of the respective powders are shown [15]. 63

64 Acknowledgments We acknowledge funding from the EU-FP7- NANOANTENNA project GA Development of a high sensitive and specific nanobiosensor based on surface enhanced vibrational spectroscopy and the PRIN 2008 project 2008J858Y7_004 Plasmonics in self-assembled nanoparticles / Surface Enhanced Raman Spectroscopy on self-assembled metallic nanoparticles. References Figure 4: SERS of buffered biomolecules solutions (blue lines) compared to Raman spectra of the respective powder and to the Raman spectra of the same solution in absence of gold aggregates: (a) Lysozyme in PBS at 1 M, (b) Phenylalanine in PBS at 1 mm and (c) Manganese Superoxide Dismutase at 0.1 mm. [1] M. Moskovitz, Rev. Mod.Phys. 1985, 57, 783. [2] S. Nie and S. R. Emory, Science 275 (1997) [3] K. Kneipp et al., Chemical Physics 247 (1999) 155. [4] K. Kneipp, M. Moskovits and H. Kneipp, Surface Enhanced Raman Scattering; Springer: New York, [5] E. Le Ru, P. Etchegoin, Principles of Surface Enhanced Raman Spectroscopy; Elsevier: Amsterdam, [6] F.Svedberg et al., Nano Lett., 6 (2006) [7] F. Svedberg et al., Faraday Discuss., 132 (2006) 35 [8] L. Tong, Lab Chip, 9 ( 2009) 193. [9] M. J. Guffey and N. F. Scherer, Nano Lett., 10 (2010) 4302 [10] M. J. Guffey and N. F. Scherer, Proc. of SPIE, Optical Trapping and Optical Micromanipulation VII, edited by Kishan Dholakia, Gabriel C. Spalding (2010) Vol [11] P. H. Jones et al., ACS Nano 3 (2009) [12] M.B. Mohamed, J. Phys. Chem B., 102 (1998) 9370 [13] A. Kaminska et al., Phys Chem Chem Phys 10 (2008) [14] A. Kaminska et al., Journal Raman Spect 41 (2009) 130. [15] B. Fazio, C. D Andrea, V. Villari, N. Micali, O. Maragò, M.A. Iatì, G. Calogero, P.G. Gucciardi, in preparation. Conclusions In summary, we implemented a SERS biosensor based on photothermally aggregated gold nanorods, operating in liquid environment. This in situ aggregation process has been applied for the Raman detection of Bovine Serum Albumin (BSA) molecules in Phosphate Buffer Solution (PBS) at concentration down to 10-7 M. The method has been successfully validated for the SERS detection other molecules of biological interest in their natural habitat, as Phe, Lyz and MnSOD, the latter being a precious biomarker in medical diagnosis. 64

65 MISSING RESONANCES AT THE BGO-OD EXPERIMENT F. Curciarello a,b,*, V. De Leo a,b, G. Mandaglio a,b, M. Romaniuk a,b,c, G. Giardina a,b a)dipartimento di Fisica, Università di Messina, I-98166, Messina, Italy b) INFN-Sezione Catania, I-95123,Catania, Italy c)institute for Nuclear Research, National Academy of Science of Ukraine, Kiev, 03680, Ukraine *Corresponding author, Abstract The excited states of nucleons are mostly treated in the framework of the so-called constituent quark model. This model has been very successful in describing mesons and baryons into the well known multiplet structures and in the prediction of the hadronic excitation spectrum by few parameters. However there are some problems concerning the description of the observed baryon resonance spectrum by the constituent quark model. One problem is due to the so-called missing resonances : much more excited states of the nucleon are predicted by the model than the ones have been observed in experiments. It is unknown if this mismatch is caused by experimental limits or by the models used to describe the nature of quarks bonds inside nucleons. Indeed the choice of the theoretical model is of basic importance to fix the effective degrees of freedom of the constituent quarks and therefore the number of possible excited states of nucleon. For this reason other quark models have been proposed as the di-quark model and the flux-tubes model. The only way to establish the proper effective degrees of freedom is to test the theoretical predictions with experiment[1-2-3]. In the present paper will be presented the specific program of the BGO-OD experiment at ELSA of Bonn in the missing resonances research. The international experiment BGO-OD (INFN-MAMBO experiment) consists of a 4πelectromagnetic calorimeter, different charged sensible detectors for tracking particles, an open dipole spectrometer for charged particles and momentum reconstruction. That experiment, thanks to the high photon luminosity (10 7 s) of energy up to 3.2 GeV produced by electron bremsstrahlung of the ELSA cyclotron, represents a new experimental information source devoted to investigation of the missing resonances puzzle. Introduction The availability over the last decade of high dutycycle accelerators coupled with the use of large solidangle detectors yielded a wealth of experimental information in the field of the photo- and electroproduction of mesons from the nucleons. The attempt is to extract, from photoproduction, the electromagnetic couplings and furthermore the hadronic properties of the excited nucleon states that cannot be accessed via pion scattering, either because the resonances largely overlap, or because of a weak coupling to the single pion-nucleon channel. The energy scale which is typical of the nucleon and its resonances is the low energy regime where a perturbative approach of the QCD theory is not possible because of the strong coupling constant becomes large. This situation offers both a challenge and a chance: we do want to understand the physics laws governing the bilding blocks of the matter at low energies, in the regime where we encounter them in the nature, on the other hands is obvious that the complex many-body system nucleon offers the ideal testing ground for concepts of the strong interaction in the non-perturbative regime. Therefore the most important step toward the understanding of the nucleon structure is the identification of the effective degrees of freedom which naturally must reflect the internal symmetries of the underlying fundamental interaction. This step is attempted in the framework of the constituent quark model[4-5-6] which have contributed Fig. 1 Effective degrees of freedom in quark models: three equivalent constituent quarks, quark-diquark structure, quark and flux tubes substantially to our understanding of the strong interaction. The classification of the mesons and baryons in the well known multiplet structures as derived from the symmetry, and the description of the hadronic excitation spectrum with only few fitting parameters were striking success of this model. Most of the models start from three equivalent constituent quarks in a collective potential. Here the quarks are not point-like but have electric and strong form factors. The potential is generated by a confining interaction, for example in 65

66 the flux tubes picture, and the quarks interact via a short range residual interaction. This fine-structure interaction, usually taken as color magnetic dipoledipole interaction mediated via one-gluon-exchange (OGE) is responsible for the spin-spin and spin-orbit terms. However, alternative models were developed. Indeed, models have been proposed that are based on a different number of degrees of freedom (see fig.1). One group of models describes the nucleon structure in term of a quark-diquark (q-q 2 ) cluster[7], if the diquark is sufficiently strongly bound, low lying excitations of the nucleon will not include excitation of the diquark. Therefore, these models predict a fewer low-lying states of the nucleon than the conventional quark models. On the other hand other models predict an increased number of excitation states with respect the usual constituent quark model[8-9]. The choice of the theoretical model to describe nucleon structure is of crucial importance because the number of excited states with defined quantum number (baryon resonances) follows directly from the number of effective degrees of freedom of quarks inside nucleon. Consequently a comparison of the experimentally excitation spectrum to model predictions can allow us to determine the correct number of degrees of freedom and so to understand the nature of quark bonds and its interaction inside the nucleon. However, from an experimental point of view the situation is quite different from atomic and nuclear physic. The dominant decay channel of a nucleon resonance is the hadronic decay via emission of mesons (see fig. 2). Thus, the lifetimes of the excited states are typical of the strong interaction (η~10-24 s) with corresponding widths of few 100 MeV. The spacing of the resonances is often no more than a few 10 MeV so the overlap is very large, this makes difficult to identify and investigate individual states. more states are predicted than have been observed. It is unknown if this evidence is related to an inept determination of effective degrees-of-freedom in the theoretical models or if it is an experimental limit. One hypothesis of this mismatch is the decoupling of many resonances from the partial wave analysis of pion scattering. This resonances can be found when other initial and/or final states are investigated. In fact, recent quark models predict a number of unobserved resonances to have large decay branching ratios for the emission of mesons other than pions. To observe this states, nucleon should be excited by scattering of respective mesons. However, most of them are short lived so the preparation of secondary beams becomes impossible. The use of induced reactions by electromagnetic interaction offers an alternative. The progress made in accelerator and detector technology during the last fifteen years has considerably enhanced our possibility to investigate the nucleon with different probes. In particular, the new generation of electron accelerators, like ELSA in Bonn, are equipped with tagged photon facilities and state-of-art detector systems. Fig.3 Overview of the ELSA facility in Bonn which produce a photon beam up to 3.2 GeV with the bremsstrahlung technique. Fig.2 Representation of a photoproduction of meson through an intermediate state of nucleon resonance of defined isospin I and angular momentum J. The most widely used reactions for the study of nucleon resonances use beams of long-lived mesons. However the exclusive use of pion induced reactions would bias the data base for resonances coupling weakly to the Nπ channel. Indeed, a comparison of excitation spectrum predicted by modern quark models to experimentally established set of nucleon resonances results in the problem of missing resonances : many At ELSA facility the tagged high energy photon beam is produced through the bremsstrahlung technique: electron beam from accelerator impinges on a radiator, scattered electrons produce bremsstrahlung with the typical spectral distribution 1/E γ, with energy up to 3.2 GeV. The purpose of the experiment is to study a wide class of reactions induced by photons on nucleons and nuclei with production of pseudoscalar mesons (π 0,η), pseudovettorial mesons (ω, ρ, θ) and the precise determination of the properties of baryonic resonances, in the energy region from threshold to 3.5 GeV using a polarized gamma-ray beam and/or polarized targets. 66

67 The activities will be held in Bonn in the B1project[10] at the Physikalischen Institute of the Rheinischen Friedrich Wilhems-Universität. The involved groups and organisations are coming from Russia, Ukraine, Italy and Germany. First data taking is scheduled for the biginning of the next year. BGO-OD experimental set-up A schematic view of the experimental apparatus installed in the beamline S-Bonn[11] is shown in fig. 4. The experimental setup is a combination of an opendipole forward spectrometer optimized for the detection of charged particles and of a large solid angle ( degrees) detector, the BGO crystal ball, that covers the central angular region and is optimized to detect neutral particles. This particular set-up configuration is well designed to allow the investigation of photoproduction reactions and discrimination of multi-particle final states with different charges. Dipole field together with multiple tracking sections allows for momentum/charge analysis of reaction products not possible in previously experiments. The polar angular region of small angles, θ<12, is covered by B1 magnetic spectrometer that produces a dipolar field of about 0.5 T and that will be used for the separation, identification and reconstruction of the momentum (resolution 0.5%) of charged particles emitted in the photoproduction process. For this purpose, the spectrometer is equipped with: a first track scintillating fibers detector (MOMO detector in fig.4) made of 672 fibers arranged on 3 layers, which allow to have a spatial resolution of 1,5 mm; an aerogel Cĕrenkov detector for the discrimination of charged pions from protons and particulary from charged kaons in the MeV/c range; a second track scintillating fibers detector (SciFi2) that consists of 640 scintillating fibers arranged in 4 circular layers; two set of double plane drift chambers for particle tracking, placed at the exit of the dipole; a time-of-flight detector (TOF) which provides time flight measurements for charged particles and neutrons. The central region is covered by: the BGO, (Bi 4 Ge 3 O 12 ), an homogeneous electromagnetic calorimeter made of 480 truncated pyramidal crystals placed inside 24 carbon fiber baskets each one containing 20 crystals and supported by an external steel structure. Each crystal is 24 cm long (21 radiation lenghts) and provides an high energy resolution for photon detection ( 3% FWMH at 1GeV) a good response for proton with energy up to 400 MeV and a good neutron detection efficiency. The angular resolution is of about 6-8 degrees. The characteristics of the response time of the calorimeter allow to use the signal for the experimental trigger. Each crystal is coupled to one phototube for the read out of the signals. The detector is property of INFN and used in the GRAAL experiment closed at the end of 2008; a crystal barrel detector, made of 32 plastic scintillator bars, which allows, through measurement of ΔE, the discrimination between charged and neutral particles and, in combination with the information of energy released in the calorimeter, the identification of charged particles (protons and pions); multi wire proportional chambers (MWPC's) for inner tracking; multi resistive proportional chambers (MRPC's) for forward tracking; target of H 2 or deuterium that is tight enclosed by the BGO. Fig.4 Overview of BGO-OD experimental setup at the beam line S Physical program The principle aim of this experiment is the systematic investigation of the photoproduction of mesons off the nucleon. These processes are related to the structure of both, the mesons and baryons involved, whose nature of strong bonds must still be considered as poorly understood. Only such improved experiments will shed new light on the low-energy hadronic aspects of the strong interaction. Polarisation measurements are indispensable to characterize the relevant degrees of freedom in the production process of the different mesons, in particular the formation and role of the missing resonances. Therefore, meson photoproduction provides an ideal tool to investigate particular baryonic states which challenge the quark model through their unusual features. The 67

68 photoproduction of mesons off the nucleon provides also access to several aspects of low-energy strong interaction. The mechanisms involved are not clear, in many cases not even the relevant degrees of freedom, from which resonance spectra depend. Of particular interest are the excitation and subsequent decay of baryon resonances, as well as intermediate particle exchanges in the production process, especially important in vector-meson production. To achieve one of the central goals of low-energy hadron physics, to disentangle and understand the complicated nucleon resonance spectrum, a better understanding of the meson production mechanisms is an indispensable prerequisite. It is also the basis to understand the features and hence the structure of individual states which in a striking manner do not fit to the description of quark models. Open problems are: (i) the mechanism and the relevant degrees of freedom in the photoproduction of mesons, (ii) the contrast between the general spectroscopic success of quark models and the vast discrepancy between expected and observed number of states, (iii) the structure of some well established resonances which is still not well understood. In order to try to solve these problems, processes beyond single pion photoproduction must be investigated. Final states that involve multiple pions, η, η', K, K*, ω and θ mesons, or combinations thereof (it should be stressed that some of this mesons have masses bigger than photon beam maximum energy). It is clear that progress in this field means approaching to an understanding of the complex nature of the deepest bonds of matter known so far. Experimentally, the new B1 magnetic spectrometer will provide high resolution and good particle identification for charged final states, in particular for K ±. Since the acceptance of the spectrometer extends to almost 0-degree forward direction, it is ideally suited to investigate θ production through simultaneous K + and K - detection. Moreover, the high resolution detection of recoil protons may not only add to our understanding of the basic production process, but also favour precision measurements regarding the in-medium properties of the ω meson. Finally, combination of the crystal calorimeter and the forward spectrometer yields a unique instrument for complicated multi-particle final states and in this way gives us access to the study of a wide range of phenomena in particle physic. BGO CALIBRATION-EQUALIZATION In this paragraph we report an overview on the calibration-equalization operations performed on the BGO calorimeter crystals. We performed not a simple calibration of BGO crystals but, more important, we also made an equalization of crystals varying high voltage applied to phototubes to homogenize their response. The operations can be performed by remote and still continuing now in Messina. Fig.5 Scheme of the experimental calibration chain In fig.5 we can see a roughly representation of the experimental chain of calibration: the output signal from the phototube, coupled to the crystal, is sent to a mixer reducing its amplitude and then reaches the ADC module for the readout. We worked on the calibration of 64 crystals at time of the 480 crystals (four ADC available for acquisition with 16 channel each one, in future with a full equipped BGO elettronics, we will have 30 ADC to acquire simultaneously signal from the 480 crystals). For the calibration we used three sources of 22Na, located inside the BGO cylindrical hole, which is characterized by two emission peaks: the first at MeV and the second at MeV. In order to derive the calibration constants for each channel, we tried to fix the energy of the second peak at the channel 480 of the ADCs, we also made an equalization of the crystals by changing the high voltage applied to the fototubes in order to obtain the response, (calibration peak), at the same channel of ADC for all crystals. The calibration constant is about MeV/ channel. The peaks have also been monitored in time and the fluctuations of the position of the second peak, due to the fitting procedure and to the response of crystal+adc to the source, is of about 1-2 channels corresponding to about MeV. This means an incertitude of about 1,6%-3,2% of the energy. The intrinsic resolution of the BGO+ADC at MeV is about 25%-30%. 68

69 BIBLIOGRAPHY Fig.6 Example of signal acquisition [1] A. Fantini et al. Phys. Rev. C 78, (2008); [2] R. Di Salvo et al. Eur. Phys. J A 42,151 (2009); [3] G. Mandaglio et al. Phys. Rev. C 82, (2010); [4] M. Gell-Mann, Phys. Lett. 8 (1964) 214; [5] O.W. Greenberg, Phys. Rev. Mt. 13 (1964) 598; [6] R.H. Dalitz, Proceedings of the XII Int. Conf. On High Energy Physics Berkeley, Calif. (1966); [7] M. Anselmino et al., Rev. Mod. Phys. 65 (1993) 1199; [8] R. Bijker, F. Iachello, A. Leviatan, Ann. Phys. 236 (1994) 69; [9] R. Bijker, F. Iachello, and A. Leviatan, Phys. Rev. D 55 (1997) 28; [10] [11] 69

70 70

71 RESONANT LASER ABSORPTION AND SELF-FOCUSING EFFECTS PRODUCING PROTON DRIVEN ACCELERATION FROM HYDROGENATED STRUCTURES M. Cutroneo 1,2 and L. Torrisi 1 1 Dottorato di Ricerca in Fisica, Università di Messina, V.le F. Stagno D Alcontres 31, S. Agata (ME), Italy 2 Centro Siciliano di Fisica Nucleare e Strutt. della Materia, V.le A. Doria 6, Catania, Italy * Corresponding author, mari.cutroneo@unime.it Abstract Resonant laser absorption and self-focusing effects were investigated as two typical non-linear processes occurring inside laser generated non-equilibrium plasmas. The ion emission in laser-generated plasma is dealt at low and high intensities from W/cm 2 up to values higher than W/cm 2. The properties of plasma are strongly dependent on the time and space, laser parameters (intensity, wavelength, pulse duration, spot dimension, focal position ), target composition (polymers, metals, ceramics) and target geometry (thickness, spot/thickness ratio, surface curvature, ). A considerable interest concerns the energetic and intense proton generation for the multiplicity use that proton beams have in different scientific fields (Nuclear Physics, Astrophysics, Bio-Medicine, Microelectronics, Chemistry, ). Measurements have been performed at INFN-LNS in Catania and at PALS Laboratory in Prague, by using low and high laser pulse intensities, respectively. Thick and thin targets and different detection techniques of ion analysis have been employed. The mechanisms of resonant absorption of the laser light, produced in specific targets containing nanostructures with dimensions comparable with the wavelength and high electron density, enhances the proton yield and the proton kinetic energy as result of resonant absorption effects. The mechanisms of self-focusing, obtained by changing the laser focal distance from the target surface, increase the local intensity due to further focalization the laser light in the dense vapour and consequently the plasma temperature, the density and Coulomb ion acceleration. Real-time ion detections were carried out through Thomson parabola spectrometer (TPS) coupled to a multi-channel-plate (MCP). Ion collectors (IC), SiC detectors and ion energy analyzer (IEA) have been also employed in time-of-flight configuration (TOF) technique. The energy and the amount of protons and ions increase significantly when the two investigated nonlinear phenomena occur, as it will be discussed. Introduction The interaction of short laser pulses with solids has become an important field of study because of many applications, such as the fast ignition scheme of inertia confinement fusion, the plasma-based particle accelerator, coherent x/ -ray sources, etc.. For most of these applications, the nature of the absorption process must be determined. The density scale length of the plasmas generated from the target surfaces can be estimated as: L c (1) s p where c s is the ion sound speed and p is the laser pulse duration [1]. For high intensities (> W/cm 2 ) and very short pulses (< 1 ps)) the scale length is too short to generate sufficient absorption effects and resonance absorption at the critical surface is suggested to be one of the major absorption mechanisms. Some experiments show that it plays an important role even for plasmas with a scale length considerably shorter than the laser wavelength 0. However many theoretical works on resonance absorption are valid for the case in which L > 0 [2]. At higher laser intensity the electrons being pulled out by the ponderomotive forces and then returned to the plasma at the interface layer by the wave field can lead to a phenomenon like wave breaking. Thus, the electron plasma wave is hard to develop and vacuum heating tends to be dominant [3]. A simple model is used to calculate the energy absorption efficiency when a laser of short pulse length impinges on a dielectric slab that is doped with an impurity with a resonant line at the laser frequency. It is found that the energy absorption efficiency is maximized for a certain degree of doping concentration (at a given pulse length) and also for a certain pulse length (at a given doping concentration). Absorption processes are generally dependent on the density scale length. Interaction of the laser radiation above some threshold intensities with a plasma of defined properties may significantly increase the charge state and energy of the produced ions, due to a peculiar 71

72 effect occurring in the plasma, which focalizes further the laser pulse (self-focusing effect) acting so as a small vapor lens placed in front of the target surface. Advances in laser technology have recently enabled the observation of self-focusing in the interaction of intense laser pulses with plasmas. Self-focusing in plasma can occur through thermal, relativistic, and ponderomotive effects [4]. Thermal self-focusing is due to collisional heating of plasma exposed to electromagnetic radiation: the rise in temperature induces a hydrodynamic expansion, which leads to an increase of the refraction index and further heating. Relativistic self-focusing is caused by the mass increase of electrons traveling at speed approaching the speed of light, which modifies the plasma refractive index, depending on the electromagnetic and plasma frequencies. Ponderomotive self-focusing is caused by the forces which push electrons away from the region where the laser beam is more intense. Both non-linear effects of resonant absorption and self-focusing were investigated in order to produce high yield of energetic proton emission from laser irradiated targets, as will be presented and discussed. IEA spectrometry [7]; the electronic plasma temperature, n e, was measured through the evaluation of the ablation yield (atoms removed from the laser crater per laser shot) and the volume of the visible plasma observed by a fast CCD camera. A Thomson parabola spectrometer (TPS) couplet to a multi-channel plate (MCP) was also employed at PALS in forward direction along the normal to the target surface in order to separate the different ions contributions by means of magnetic deflection by using a magnetic field of the order of 0.1 Tesla and an electric deflection of 3 kev/cm. A scheme of the TPS is reported in Fig. 3b. TPS measures the energy, charge states and ion species of ejected particles from plasma for comparison with simulation programs. Finally, a streak camera was employed at PALS to measure the laser focal position (FP) distance with respect to the target surface. Negative distances mean a focus in front of the surface while positive distances mean a focus inside the target. Experimental set-up The main experiments have been performed by using the Nd:Yag laser of INFN-LNS in Catania and the Iodine Asterix laser of PALS Laboratory in Prague. The first has been employed at 1064 nm, 9 ns pulse duration, 800 mj maximum pulse energy, with intensities between 10 8 and W/cm 2. The second has been employed at 1315 nm (1 ), 300 ps pulse duration, 600 J maximum pulse energy, with intensities between and W/cm 2. In order to generate protons, the irradiated targets were thick and thin hydrogenated solids. Many of these were polyethylene based (CH 2 -monomer) with additions of nanostructures such as carbon-nanotubes (CNT), of length of the order of 1 micron, and oxides (such as Fe 2 O 3 ). Other targets consisted of hydrogenated Si, thin films of mylar covered by Au or Al films, hydrates and metals. Generally thick films (1 mm thickness) were used at LNS for irradiation at low laser intensities to generate backward directed plasmas, while thin films (of the order of 1 micron in thickness) were employed at high laser intensity at PALS in order to generate forward directed plasmas. Time-of-flight (TOF) measurements have been obtained with ion collectors (IC), semiconductor detectors based on SiC, and electrostatic deflector ion energy analyzer (IEA) that permits to measure the average ion energy, the ion energy and the charge state distributions, respectively. Details on IC, SiC and IEA detector are given in literature [5,6]. The ion plasma temperature, T i, was measured though the Coulomb-Boltzmann shifted (CBS) fit of the experimental ion energy distributions given by the Fig 1. Typical IC spectra obtained at low intensity relative to pure polyethylene irradiation (a) and typical resonant absorption obtained by irradiating CNT nanotubes, 0.1% in concentration, embedded in polyethylene (b). 72

73 Yield (V) Activity Report 2011 Dottorato di Ricerca in Fisica, Università di Messina Results At low intensities, of the order of W/cm 2 a typical spectrum of ions emitted from polyethylene and detected by IC shows a large and slowly peak due to the carbon charge states and a faster peak due to protons, as reported in Fig. 1a. Fig. 2: Typical proton energy distribution relative to the ion emission from low intensity laser irradiation of pure polyethylene (a) and relative to that from Silicon hydrogenated nanospheres target irradiated in the same experimental conditions (b). In this case the TOF distance is 60 cm, thus the corresponding proton peak energy is about 75 ev. Pure polyethylene shows a low absorption coefficient to 1064 nm and a low electron density. Embedding CNT nanostructures in polyethylene the absorption coefficient changes strongly thus the result of the ion emission at low laser intensity, also, as reported in Fig. 1b. The SEM photo of the carbon nanotubes is reported in the inset of the figure. In this case the TOF length was 150 cm thus the corresponding maximum proton energy, calculated at the FWHM of the proton peak, is about 120 ev. The comparison between the two spectra shows that the proton/carbon ratio increases from 0.05 in pure polyethylene up to 1.5 for 0.1% concentration of CNT. Thus the insertion of absorbent nanostructures, with length comparable with the laser wavelength, produces effects of resonant absorption that can be responsible of the strong increment of the proton yield emission while a negligible proton kinetic energy increment is recorded. However, significant increment of the proton energy can be obtained using other special nanostructures inducing resonant absorption effects. At low laser intensity, a typical energy distribution of the protons emitted from an irradiated polyethylene target is reported in Fig. 2a. It gives average proton energy of about 100 ev. For comparison, the proton energy distribution obtained by irradiating amorphous surface layers of hydrogenated silicon (Si:H) with 100 nm diameter nanospheres is reported in Fig. 2b. The SEM photo of the nanospheres is reported in the inset of the figure. It gives maximum proton energy above 1.5 kev. This result may be due to a strong resonant effect generated by the high electron density of the first layers of the high absorbent target. At high intensity, of the order of W/cm 2, the produced plasma show high electron densities and the resonant absorption effects becomes more probable. A typical spectrum of ions emitted from CNT nanotubes embedded in PMMA target is provided by the Thomson Parabola spectrometer placed in forward direction along the normal to the target surface. The comparison of the experimental parabolas (Fig. 3a) with the simulation spectra (Fig. 3c) allows us to evaluate the particle masses, energy and charge states. The spectra indicates a maximum proton energy of 1.5 MeV namely, higher value than those determined by using polyethylene targets without nanotube inserted. The complexity of the laser interaction mechanisms with solid targets is due to the non-linearity of the processes occurring in the pre-plasma and of the plasma non linear optical properties which are dependent on the laser intensity and that occurs generally above a threshold of about W/cm 2 [8]. Self-focusing effects, for example, increases the intensity of the part of laser beam on the target due to the higher focusing which may reduce the spot up to dimensions comparable with the laser wavelength. Evidence of the self-focusing occurrence may be given by IEA spectrometer of the emitted particles indicating ion energy, masses and charge states. The plot of the ion yield versus the focal position indicates that for low charge states ions are due to ionization by thermal electrons generated by inverse bremsstrahlung mechanism. In contrast, ions with higher charge states, connected with the presence of fast electrons, and generated by resonant absorption mechanisms, create a maximum yield, kinetic energy 73

74 a) C 2+ C 3+ C 4+ C 5+ and charge sates when the laser focal position if placed near and in front of the target surface. D1 Thomson Parabola Spectrometer b) a) L12 Pinholes D2 S N B L1 gm L2 E -V/2 +V/2 Ld1 ge Ld2 z C 1 + C 2+ C 3+ C 4+ C 5+ C 6+ H + c) Detector x c) s In the dense vapor generated in front of the target, in facts, the ambipolar acceleration of ions due to non linear forces, including ponderometive relativistic and self-focusing, which lead to very high laser intensity in a self-focused channel may become the main reason for the presence of high kinetic energy and high charged ions. Such a result was ascribed to the volume effect of produced plasma due to the interaction of continuously decreasing diameter of the laser beam with respect to the target surface that, in the case of self-focusing mechanisms, is found to a forward negative focus position. Fig. 4a shows a typical example of IEA spectrum obtained by irradiating Au target in no condition of self-focusing, when the focal position is FP = m, with the focal position inside the target and high spot dimension. In such conditions the self-focusing cannot happen because the intensity is below the threshold value and the number of charge states is only six. The inset of the figure shows a streak camera X-ray image and a scheme indicating with high precision the used focal position. Fig. 4b shows a typical example of IEA spectrum in conditions of self-focusing, when the focal position is FP = -200 m. In such conditions the number of charge states is about 56 as result of hotter energetic plasma. Also in this case the inset of the figure shows the streak camera X-ray image and the scheme indicating the used focal position. This last effect occurs because the high light refraction effect produces a further laser beam focalization, due to the dense plasma volume in front of the target, which converges the beam so as a focusing lens. At higher intensities the data were collected from literature and compared with our measurements in order to evaluate the generalized law of I 2 scale factor [9]. Generally a linearity of processes occurs with the law I 2, however over linear dependences occur when resonant absorption and self-focusing take place. H+ E p = 1.5 MeV Fig. 3: Typical experimental spectrum related to Thomson Parabola placed in forward direction with respect to the thin target with nanostructures embedded in polyethylene (a), scheme of the TPS spectrometer (b) and comparison with the parabola simulation plot (c). Discussion and conclusions The existence of an optimum laser focus position for generation of the fastest ions with the highest charge states in front of the target surface is consistent with literature [10]. The course of dependencies and similar values of the highest Z max indicate a threshold for the appearance of relativistic self-focusing of laser beam and a principal limitation of the maximum attainable laser intensity. At PALS differences for 1 and 3 could be ascribed to a different absorption of laser radiation, in accordance with the scaling relation I 2. The front part of the 300 ps laser pulse interacts with the target and creates an expanding plasma plume. Considering for simplicity, the expansion velocity v = 74

75 10 6 m/s, the plasma plume attains the distance of 100 m within the first 100 ps. For the laser beam diameter of 70 m, the self-focusing length should be about 100 to 200 m, at least. For FP = 0, the more the plasma plume expands, the longer the interaction length, but the lower the laser intensity with which the front of the plasma interacts. NO SELF- FOCUSING a) The following conclusions can be made: Nano and micrometric structures, such as carbon nanotubes, polymeric chains and molecular groups with dimensions comparable with the laser wavelength may induce resonant absorption effects increasing the plasma temperature and the acceleration ion drive mechanisms; Resonant effects seem to be influenced by structure and composition of the target, by the plasma frequency and occur at high intensity and in the contrary of the literature also at low intensities, like we showed in this work. Self-focusing processes influence significantly the generation of ions with the highest charge states, using high power iodine laser with the pulse length of 300 ps and an optimal FP distance can be found to enhance this effect of intensity increase due to the focal spot decreasing. Acknowledgements Work supported by LaserLabEurope (Project No.: pals ) and by INFN-LIANA Project. SELF- FOCUSING EFFECT TOF ( s) Fig. 4 Typical IEA spectrum obtained at high intensity laser at PALS laboratory in Prague relative to Au target irradiated in no selffocusing condition (a) and in self- focusing condition (b). b) References [1] H. Cai, W. Yu, S. Zhu, C. Zheng, L. Cao, B. Li, Z. Y. Chen and A. Bogerts, Physics of Plasmas 13, , 2006; [2] W. L. Kruer, Physics of Laser Plasma Interactions Addison- Wesley, New York, 1988; [3] S. C. Wilks and W. L. Kruer, IEEE J. Quantum Electron. 33, 1954, 1997; [4] L. Torrisi, D. Margarone, L. Laska, J. Krasa, A. Velyhan, M. Pfeifer, J. Ullschmied, L. Ryc Laser and Particle Beams 26, , 2008; [5] E. Woryna, P. Parys, J. Wolowski, and W. Mroz, Laser Part. Beams 14, 293, 1996; [6] L. Torrisi, G. Foti, L. Giuffrida, D. Puglisi, J. Wolowski, J. Badziak, P. Parys, M. Rosinski, D. Margarone, J. Krasa, A. Velyhan and J. Ullschmied J. Appl. Phys. 105, , 2009; [7] L. Torrisi, S. Gammino,L. Andó, L. Laska, J. Krasa, K. Rohlena, and J. Ullschmied, J. Wolowski, J. Badziak, and P. Parys J. of Appl. Physics 99, , 2006; [8] L. Laska, L. Ryc, J. Badziak, F.P. Boody, S. Gammino, K. Jungwirth, J. Krasa, E. Krousky, A. Mezzasalma, P. Parys, M. Pfeifer, K. Rohlena, L. Torrisi, J. Ullschmied and J. Wolowski Rad. Eff. & Def. in Solids 160 (10 12) (2005) ; [9] L. Laska, K. Jungwirth, J. Krasa, E. Krousky, M. Pfeifer, K. Rohlena, J. Ullschmied, J. Badziak, P. Parys, J. Wolowski, S. Gammino, L. Torrisi and F.P. Boody, Laser and Particle Beams 24(1), , 2006; [10] L. Laska, K. Jungwirth, J. Krasa, M. Pfeifer, K. Rohlena, J. Ullschmied, J. Badziak, P. Parys, L. Ryc, J. Wolowski, S. Gammino, L. Torrisi and F.P. Boody, Czech. J. of Physics 55 (6), ,

76 76

77 BARYON SPECTROSCOPY BY VECTOR MESON PHOTO-PRODUCTION AT BGO-OD EXPERIMENT V. De Leo a, b,*, F. Curciarello a,b, G.Mandaglio a,b, M.Romanyuk a,b,c, G.Giardina a,b. a)dipartimento di Fisica, Università di Messina, I-98166, Messina, Italy b)infn- Sezione Catania, I-95123,Catania, Italy c)institute for Nuclear Research, National Academy of Science of Ukraine, Kiev, 03680, Ukraine * Corresponding author, vdeleo@unime.it Abstract The study of baryon resonances plays the same role for understanding of the nucleon structure as the nuclear spectroscopy was for the investigation on the atomic nucleus structure. Excitation energies and quantum numbers of the low lying nucleon resonances are well known. Properties like mass, spin, and parity alone, however, do not offer stringent tests of hadron models. Much more crucial tests are provided by the investigation of transitions between the states, which reflect their internal structure. The dominant decay channel of nucleon resonances is the hadronic decay via meson emission. Photo-production of mesons, which carries information on strong and electromagnetic decay properties, therefore provides a very valuable tool for their study. The progress made in the last years in accelerator and detector technologies has largely enhanced our possibilities to investigate the nucleon with different probe. The new generation of electron accelerators equipped with tagged photon facilities have opened the way to meson photoproduction experiments of unprecedented sensitivity and precision. The possibilities of the starting international experiment BGO-OpenDipole (linked to the I.N.F.N. MAMBO experiment) at the ELSA facility of Bonn, which involves the hardware testingimprovement and software production contributions of the Messina group will be described in detail in the present report. The experiment represents a new sophisticate electromagnetic probe for the investigation of baryon resonances by the meson decay detections. Introduction Current issues in the understanding of the strong interaction address the structure of hadrons, consisting of quarks and gluons, as the building blocks of matter. Central challenges concern the questions why quarks are confined within hadrons and how hadrons are constructed from their constituents. One goal is to find the connection between the parton degrees of freedom and the low energy structure of hadrons leading to the study of the hadron excitation spectrum but the excitation spectrum of the system does not provide very sensitive tests of models [1]. The crucial tests come from the investigation of transitions between the states which are more sensitive to the model wavefunction. The dominant decay channel of nucleon resonances is the hadronic decay via meson emission to the nucleon ground state [2]. However, photon decay amplitudes are also of great interest since the photon couples only the spin flavor degrees of freedom of quarks and therefore reveals their spin-flavor correlation which are related to the configuration mixing predicted by the QCD [3]. Perturbative QCD at high energies deals with the interactions of the quarks and gluons. However, our picture of the nucleon has much more to do with effective constituent quarks and mesons that somehow subsume the complicated low energy aspects of the interaction which generate the nucleon many body structure of valence quarks, sea quarks and gluons. The most important step towards an understanding of nucleon structure is therefore the identification of the relevant low-energy effective degrees of freedom. Most nucleon models are based on three equivalent constituent quarks interacting via some QCD inspired interaction. However, models based on quark-diquark (q q 2 ) configurations were also suggested and more molecular-like pentaquark ( qqq qq ) structures have been discussed in the context with certain nucleon resonances. From the experimental point of view the main difference between nuclear and nucleon structure studies results from the large, overlapping widths of the nucleon resonances and much more important non resonant background contributions which both complicate detailed investigations of the individual resonances. The existing data for nucleon resonances were mostly determined by πn scattering. The comparison of the set of resonances predicted by modern quark models with the set of experimentally established resonances resulted in the so-called missing resonances problem [4]: more resonances are predicted than observed. This problem encouraged the use of the photo-production of mesons as an alternative tool to excite the resonances. The advent of a new generation of electron accelerators allowed to perform meson photo-production experiments of unprecedented sensitivity and precision [5]. Pion scattering on a proton target has been chosen as the best tool to excite and to study the resonances of the nucleon. Nucleonic resonances are excited states of the nucleon with large mass width but with well defined spin, isospin and parity. Their identification 77

78 and their characterization were carried out through the analysis of the pion-nucleon scattering data by partialwave phase-shifts method. In this method, the excitation of a given resonance is searched with the amplitude behaviour of a specific partial wave in a characteristic plot called Argand diagram [6]. The J π of the pseudo-scalar mesons (pions, eta, kaons) is 0. The J π of the vector mesons (rho, omega) is 1. The isospin of pions, kaons and η is 1, 1/2 and 0 respectively. The isospin is 1 for ρ and 0 for ω. All of the mesons have a short lifetime ( 10 7 s); however, π ± and K ± may have a path of several meters in the laboratory and then be detected with standard detectors similarly to stable charged particles, whereas η, η', ρ and ω decay almost at their production point. It is worth mentioning that the rare decay modes are used as special tools to test chiral perturbation theory and basic invariance principles. Experimental set-up. A schematic view of the experimental apparatus used in the S-beamline of Bonn is shown in Figure 1. The Electron Stretcher Accelerator consists of three stages (injector LINAC, booster synchrotron and the stretcher ring) and provides a beam of polarized and unpolarized electrons with a tunable energy of up to 3.5 energy GeV. The bunched electron beam impinges on a radiator. Scattered electrons produce bremmstrhalungg with the tipical 1/E γ spsectral distribution. The polar angular region of small angles (θ < 12 ) is covered by B1-magnetic field spectrometer that produces a dipolar field of about 0.5 T and that will be used for the separation, identification and reconstruction pulse resolution (0.5%) of charged particles emitted in the photo-production process. wide central hole allows the photon beam to pass through [7]. Figure 2. MOMO detector. - The aerogel Čerenkov detector (ACD) that serves to reliably discriminate pions against protons, and particularly improves the K ± identification substantially. - SciFi2 detector where an active area of 66cm x 51cm is obtained using 640 scintillating fibers with a diameter of 3mm [7]. Figure 3. SciFi2 detector. Figure 1. Schematic view of S - beamline accelerator ELSA in Bonn. For this purpose, the spectrometer is equipped with: - MOMO is a scintillating fiber vertex detector with 672 channels. It consists of three layers of 224 parallel fibers (2.5mm diameter) each. The layers are rotated by 60 against each other. The arrangement yields a circularly shaped sensitive detector area of 44cm diameter. The spatial resolution is about 1.5mm, yielding effectively more than pixels. A 5cm A central hole (4cm x 4cm) allows the beam to pass through. Groups of 16 fibers are glued together to form a so-called module. The design guarantees a minimum path length (about 2mm) for particles traversing the circular fibers. The modules are arranged in two layers twisted by 90 degrees. - Tracking of charged particles behind the spectrometer magnet is performed with eight horizontal drift chambers (DCs) which are built at the PNPI Gatchina. To cover the necessary angular range each DC has a sensitive area of at least 2456mm 1232mm. The photon beam has to penetrate the DCs. The distance of the chambers from the target will range from 3.7 m for the first chamber up to 4.7 m for the last. For accurate positioning and simplified handling the chambers will be hanging from two support beams 78

79 attached to the magnet. Four of the chambers will be rotated by ± 9 degree around the beam axis. With two of the remaining chambers having horizontal wires and the other ones vertical wires four different wire orientations are obtained. - The forward spectrometer will be complemented by a time-of-flight (TOF) detector, which is an essential component for particle identification, because it provides flight-time measurements for both, charged particles and neutrons. It has to cover the inner degree angular range at a distance of 5m downstream of the target. It consists of four walls with a 3 3 m 2 front surface, mounted on independent mechanical stands. Each wall houses 14 individual scintillating bars of 3000 mm 200 mm 50 mm size with photomultiplier readout at both ends. The polar angular region between 25 and 155 degrees is covered by: - The BGO (Bi 4 Ge 3 O 12 ) Rugby Ball is a large acceptance calorimeter designed to measure multiphoton states with excellent energy resolution. The design of the calorimeter has taken into consideration a constant thickness in every direction and a central hole of radius 100 mm for the passage of the beam, target and inner detector housing. The resulting structure is made of 480 truncated pyramidal crystals of 240 mm length (corresponding to ~ 21 radiation lengths) arranged in a matrix covering the polar angles from 25 to 155 and the whole azimuth for a total solid angle ΔΩ = 11.3 sr. The mechanical structure consists of 24 carbon fibers baskets, each containing 20 crystals, and supported by an external steel frame. Figure 4. Overhead view of the BGO calorimeter. The baskets are divided into cells to keep the crystals mechanically and optically separated. The thickness of the carbon is 0.38mm for the inner walls and 0.54 mm for outer walls. The steel support frame is separable into two moving halves to allow to access the central part of the detector [7]. - A cylinder of 32 plastic scintillator bars, which allows, trough the ΔE measure, the discrimination between charged and neutral particles and in combination with the energy released in the calorimeter, the identification of charged particles (protons and pions). - The target can be a proton or deuterium target. Hardware testing To install the BGO system in Bonn it was necessary to replace most of electronic acquisition and HV distribution system to the crystal. The reading of the BGO signal amplitude is made by sampling ADC modules 32 -channel multiplexer. The main characteristics of the ADC modules (AVM16 MAMBO) are the following: -Sampling frequency 160 MHz (= 6.25ns) -12 bit resolution (corresponding to 4096 channels) -16 signal input and one trigger input. The sampling of the signal occurs within a time interval defined by the user that can begin even before the trigger signal (in our case the time window width is 800ns). The initial samples (four) are dedicated to the determination of the baseline event subtracting automatically the value determined at the signal; the outgoing signal is thus cleaned of any background. The tests on the ADC modules were performed working with external signals and triggers, coming from a pulse generator by setting 9 different possible offset values on the baseline value. For each baseline, we have been sending a pulser signal with an amplitude varying from 100 mv to 10 mv with steps of 10 mv. The signal coming from the pulser is a wave with trapezoidal shape, time width 200 ns, rise time 5 ns, frequency 1 khz. The procedure followed for the tests with the pulser and different baselines is the following: at first no signal is sent to the ADC and the baseline offset is set; then the baseline register is read and only at this time the signal is sent to the ADC. The value of 100 mv on the pulser current is fixed and then the baseline register is read again and the acquisition program is started; thus the acquisition program is stopped and the value of 90 mv on the pulser current is fixed. As before, the baseline register is read again and the acquisition program is started; this procedure is made for ten values of current (form 100 mv to 10 mv). The test results have highlighted some problems of the ADC modules. Strong difference was shown in the extracted value of the total integral (Q tot ) with a same input signal between different modules and different channels. The response of the ADC channels to a fixed input strongly depends on the baseline offset (the response strongly increases with baseline value reaching a plateau only for the higher baseline values). The linear behavior was checked and it was confirmed for almost all baseline offset values but the strongly dependence of the gain on the baseline offsets affects the ADC linearity. Therefore, the time synchronization features between ADC modules have been verified. The tests on ADC modules have enabled their improvement. 79

80 Physics The goal of this project is the systematic investigation of the photoproduction of mesons off the nucleon. Polarization measurements are indispensable to characterize the relevant degrees of freedom in the production process of the different mesons, in particular the formation and role of hadronic resonances. The photoproduction of mesons off the nucleon provides access to several aspects of lowenergy strong interaction. The quark model predicts a large number of nucleon resonances which have not yet been observed [8]. Since the most used reaction for their study was pionnucleon scattering, one could infer that these so-called missing resonances may couple weakly to this channel[9]. One possibility to investigate this issue is the photo-production of ω mesons off the proton. This channel is interesting for several reasons: first, there is no nucleon resonance well-established decaying by ω emission; second, the threshold of ω-photoproduction lies in the third resonance region, which is less explored than the first two; third, from the sparse data in the literature and a new generation experiment, evidence for resonance excitations in γ p ωp is still not obvious. Due to the fact that the ω is isoscalar (I=0), the s- channel production of this meson is only associated with the decay of N (I=1/2) states and not the decay of Δ (I=3/2) states, which greatly simplifies the contributing excitation spectrum. However the vector meson character of the ω implies that at least 23 observables have to be measured to disentangle all contributing resonances, instead of 8 in the pseudoscalar case. It can be hoped however, that fewer than 23 observables already provide significant constraints. In any case, the measurement of polarization observables will provide important information about the production mechanism of the ω meson[10]. At high photon energies resonances play no role. The cross section of vector-meson production off nucleons falls off exponentially with the squared recoil momentum, t, corresponding to the range of the mutual interaction. The t dependence of the cross section, which is approximately the same for all sufficiently high photon energies, is characteristic for diffractive production. It is associated with the exchange of natural parity quantum numbers (Fig. 1 left) related to the Pomeron, a composite gluonic or hadronic structure. At large t deviations from pure diffraction show up. From the comparison to QCD-inspired models which are also able to describe φ and ρ 0 photoproduction, the presence of hard processes in the exchange itself was thus also included at t >1 GeV 2. Figure 5.Contributions to ω-photoproduction: natural parity t-channel exchange (left), unnatural parity π0 t- channel exchange (middle), s-channel intermediate resonance excitation (right). Because of the sizeable ω π 0 γ decay (8%), significant unnatural parity π 0 exchange has been expected for ω-photoproduction at smaller energies (Fig.1 middle). It was indeed observed and found dominating close to threshold. However, neither Poimeron nor π 0 exchange are able to reproduce the strong threshold energy dependence of the cross section and the ω decay angular distribution observed in exclusive photoproduction and electroproducton. This was interpreted as possible evidence for s-channel contributions (Fig.1 right)[11]. Experimental support comes from a first measurement of photon-beam asymmetry, Σ, through the GRAAL collaboration[6,12]. The threshold ω-photoprodution is E γ = 1.1 GeV; ω meson decays mainly into channels: 0 0 ( BR.. 89%) ( BR.. 8.9%) (1) In Bonn, the load decay channel can be observed very well by combining the BGO (π 0 ) and the spectrometer (π + π - ). Moreover, the spectrometer allows a more detailed study of other vector-meson such as the ρ-meson. Its main decay modes (to almost 100%) proceed via ρ 0 π + π -, ρ + π + π 0 and ρ - π - π 0. In particular, the last two decays that derive from the twins reactions γ p ρ + n and γ n ρ - p may be confused in case of the proton inefficiency combined with neutral noise, for this reason the BGO - spectrometer combination is crucial. REFERENCES [1] F. Wilczek, hep-ph/ v2; [2] G. Mandaglio et al., Phys.RevC 82, (2010); [3] R. Di Salvo et al., Eur.Phy. J A 42,151 (2009); [4] A. Fantini et al., Phys.RevC 78, (2008); [5] B. Krusche, Czech. J. Phys. 49 (1999); [6] E. Hourany, Romanian Reports in Physics, Vol. 59, No. 2, P , 2007; [7] [8] S. Capstick and W. Roberts, Prog. Part. Nucl. Phys. 45, S241 (2000); [9] J. Ajaka et al., PhysRevLett. 96, (2006); [10] A. V. Sarantsev, A. V. Anisovich, V. A. Nikonov and H. Schmieden, Eur. Phys. J. A 39, (2009); [11] F. Klein, PhysRevD.78, (2008); [12] V. Vegna et al., in preparation. 80

81 DIODE LASERS FOR OPTICAL TRAPPING APPLICATIONS R. Sayed a,b, *, G. Volpe c, M. G. Donato b, P. G. Gucciardi b, and O. M. Maragò b a)dottorato in Fisica dell Università di Messina, Dip.to di Fisica, F. S. D Alcontres 31, S. Agata-Messina, Italy b)cnr-ipcf, Istituto per i Processi Chimico-Fisici, V.le F. S. D Alcontres, 37, I-98158, Messina, Italy c)max-planck-institut für Intelligente Systeme, Heisenbergstr. 3, Stuttgart, Germany * Corresponding author, rania_sayed80@yahoo.com Abstract Diode lasers can be built to meet stringent specifications on beam stability, optical beam shape, wavelength stability, thermal stability, and compact dimensions. Stabilization of laser frequency is essential for various research fields such as metrology, frequency standards, and optical communications. Here we discuss how diode lasers can be employed in optical trapping applications, where a laser beam is tightly focused with a high numerical aperture objective at the diffraction limit to trap particles near its focal spot. In this context we will describe a novel approach to optical trapping based on optical feedback that can be applied with low numerical aperture lenses. focal region of the lens by the forces arising from the scattering of light by the particle [5,6] (see Fig. 1). Keywords: Diode lasers, optical feedback, frequency stabilization, optical trapping. Introduction Since their first use in atomic physics in the early 80's, diode lasers have become an important part of many modern experiments [1]. This is primarily driven by the fact that they are compact, cost effective, small sized, and highly efficient [2]. For the application of diode lasers in high resolution laser spectroscopy, linewidth reduction and frequency stabilization have been actively investigated to improve the poor spectral quality of diode lasers. In principle these systems are able to achieve high stability in their output intensity and frequency (up to ). However frequency and intensity stability are considerably dependent on operational supply current and on laser diode chip temperature. Thus it is crucial to minimize fluctuations of these operational parameters. A laser diode is very sensitive to static electricity and EM interference. Its quality shielding and galvanic separation of signal wires from supply wires is not useless complication. Our interest in diode lasers lies in their applications for novel approaches to optical trapping and laser cooling of nano and microparticles. The ability to exploit light forces for the trapping and handling of microparticles was pioneered by Ashkin [3] in the 1970 s. Some years later the first optical tweezers (OT) was realized [4] using a laser beam strongly focused by a high numerical aperture objective lens. In these systems a particle is trapped in the Fig. 1: (left) Ray optics interpretation of optical forces on a dielectric sphere. (a) A light-ray (red) exerts a force (dark gray) arising from its refraction and reflection. (b) The forces on the sphere (dark gray) due to two light-rays (red and orange) compensate each-other at the equilibrium position. (c) Restoring force on an axially displaced sphere. (d) Restoring force on a laterally displaced sphere. (right) Exemplar 2 m latex spherical particle optically trapped in our laboratory with a diode laser at 830nm. Since then, OT have been extensively used for applications in cellular and molecular biology, soft matter and nanotechnology. In biology, OT are used to make micro-mechanical experiments on cells and microorganisms both in vitro and in vivo [7-9], where the use of a near infrared wavelength (800nm-1100nm) laser prevents photodamage and thus the death of microorganisms and cells [9]. In physics, the ability to apply forces in the range of pico-newton to micro- and nanoparticles and to measure their displacements with nanometer precision is crucial for investigation of colloidal and condensed matter systems [10]. More recently OT have been also used to manipulate, rotate and assemble a variety of nanostructures, such as carbon nanotubes [11-13], nanowires [14,15], polymer nanofibers [16], graphene flakes dispersed in water [17] and metal nanoparticles [18] and aggregates [19,20]. Here 81

82 we discuss a novel application of diode laser to optical trapping based on optical feedback-locking. Theory and Overview Optical Feedback. The sensitivity of the output intensity of a diode laser to both the amplitude and phase of external feedback is well documented [21]. The effects of optical feedback on the behavior of diode laser have shown that the dynamical properties of injection lasers are significantly affected by the external feedback, depending on the interference conditions between the laser field and the delayed field (returning from the external cavity). The essence of the optical feedback method is to increase the quality factor of the laser resonator, therefore narrowing the linewidth and stabilizing the laser's wavelength [22]. It is well known that external optical feedback strongly affects the properties of semiconductor lasers, the returned light into laser cavity causes variation in the lasing threshold, output power, linewidth, and laser spectrum. Under lasing conditions, the diode cavity is filled with gain medium, which, to a large extent, compensate for the diode cavity loss. It, therefore, has substantially greater effective quality factor, and consequently, greater influence on the laser behaviors, than the passive external cavity. For this reason, the following form of field equation has been adopted for a compound cavity laser configuration, obtained by adding an external feedback term to a standard laser equation in complex form [21], that is: d E(t)e dt E(t)e Here, N i t i t i ke(t resonant frequency and cavity, N (n) )e i 1 G(n) 2 (t ) 0 (1) n is the diode cavity longitudinal mode 0 is the cavity loss of the diode is the laser oscillation frequency, E t is the field amplitude, and is the transit time in the external cavity. The last term on the right hand side represents the external feedback and the coefficient k is related to cavity parameters as, k c /2 l D (2) Where c is the speed of light, l D is the cavity length of diode laser, and is refractive index of the active region. The parameter defined with the facet and external mirror reflectivities R 2 and R 3 as 1/ 2 2 )(R3 / R2) ( 1 R (3) It is a measure of the coupling strength between the two cavities. In the above expression for external feedback, multiple reflections in the external cavity have been neglected. Optical Trapping. In an OT the trapping force arises from the presence of a gradient in the intensity of the optical field and tends to attract particles with refractive index higher than their surrounding towards the highintensity regions of the field (high-field seekers), and conversely particles with lower refractive index towards the low-intensity regions (low-field seekers) [3-6]. Using simple ray diagrams it is possible to provide a very detailed picture of the physics of the trapping process, without the need for the use of involved calculus and electromagnetic theory. As can be appreciated from Fig. 1(a), when a light ray enters a transparent dielectric sphere it undergoes deflection as a result of refraction at the interfaces. Such deflection of photons that carry momentum results in a recoil force. This force (dark gray arrow in Fig. 1(a)) however does not trap the particle; it only pushes the sphere away from the light. To trap an object it is necessary to use a set of light-rays coming from different directions. If two light-rays come from opposite sides of the dielectric sphere at a very high angle they can indeed trap the particle (Fig. 1(b)). It can be easily appreciated from similar ray diagrams what happens when the sphere is displaced both axially (Fig. 1(c)) and laterally (Fig. 4(d)) with respect to the focus. In this cases the total force (black arrow) pushes the particle towards the optical trap center arises. A simple example is a highly focused laser beam. This acts as an attractive potential well for a particle. The equilibrium position lies near but not exactly at the focus. When the object is displaced form this equilibrium position, it experiences an attractive force towards it. This restoring force is in first approximation proportional to the displacement; in other words, the force in the OT is well described by Hooke s law: F x = - K x (x - x 0 ) (4) where x is the particle s position, x 0 is the focus position, and k x is the optical trap spring constant along x, usually referred as trap stiffness. In fact, optical tweezers create a 3D potential well that can be approximated by three independent harmonic oscillators, one for each of the x, y, and z directions. In the xy-plane (perpendicular to the direction of the beam propagation) the force is mainly due to gradient optical forces, while along the z-direction (along the direction of the beam propagation) the restoring gradient force is weakened by the presence of radiation pressure that pushes the particle away from the focal spot. More complex intensity patterns have been obtained, for example, by interfering two or more light beams or by the use of advanced techniques such as holography and timemultiplexing. 82

83 Power (mw) Activity Report 2011 Dottorato di Ricerca in Fisica, Università di Messina Experimental Setup In our experiments, standard optical trapping is generally achieved by focusing a 830 nm laser beam (from a laser diode Sanyo DL , 150mW nominal power) through a 100 oil immersion objective (NA=1.3) in an inverted microscope configuration (see Fig. 2 for a sketch). The laser power available at the sample is about 20mW and is kept constant during the optical force measurements. Optically trapped particles (generally latex beads with 2 m diameter) are imaged with a CCD camera (see Fig. 1). Results and Discussion The resulting optical force in feedback-controlled optical trapping is regulated by the response of the light source to the optical feedback, so it is useful to study the characteristics of diode lasers. Three diode lasers at different wavelengths and different output power have been studied T= 18 O C 40 P 20 I I th = 33 ma Injected current (ma) Fig. 3: L.I. curve for diode laser (Sanyo DL S, 785nm, 80 mw). The measured threshold current is Ith=33 ma. Fig. 2: Sketch of the experimental setup and methodology for feedback-controlled optical trapping. (left) When no particle is trapped the optical feedback on the diode laser is on and the available power at the sample permits to efficiently attract particles at the focal spot of the low numerical aperture objective. (right) When a particle is trapped the feedback is off and the trap works at lower power. For the realization of feedback controlled optical trapping we employ a low numerical aperture objective (NA=0.5). In fact, feedback controlled trapping may release the stringent requirements on numerical aperture for the operation of standard OT. In brief, in this novel configuration (see Fig. 2) the optical feedback on the diode laser source is controlled by the light scattering from a trapped particle. When no particle is in the trap, the optical feedback from a dielectric mirror posed above the microscope objective will increase the trapping power in the focal spot. Instead, when a particle falls in the trap the optical feedback will stop and trap will work at low power preventing damage and relaxing the stringent conditions on high numerical aperture for standard OT. The most important parameter of diode lasers to be measured is the degree to which it emits light as current is injected into the device. This generates the output light versus input current known as the L.I. curve. As shown in Fig. 3 the L.I. curve for diode laser (Sanyo DL S, 785 nm, 80 mw), as the injected current is increased the laser first demonstrates spontaneous emission which increases very gradually until it begins to emit stimulated radiation, which is the onset of laser action. The exact current value at which this phenomenon takes place is typically referred to as the threshold current, I th. It is generally desirable that the threshold current be as low as possible. It is one measure used to quantify the performance of a diode laser. The second parameter we measured is differential external quantum efficiency of the diode laser η D. This is defined as the ratio between the number of photons exiting the laser ( P/hυ) to the number of electrons injected per unit time into the laser ( I/e) and it has a typical value ranging between 0.2 and 0.7 for continuous wave lasers. D P / hv e P t / e hv t where e is the electronic charge, υ is the frequency of the radiation, h is the Planck constant and P/ I is the slope efficiency of diode laser. By measuring the output power light versus current (L.I.) curve of the diode lasers Toptica photonics DL100 (403 (5) 83

84 Output power (mw) Activity Report 2011 Dottorato di Ricerca in Fisica, Università di Messina nm, 30 mw), diode laser Nichia NDHV310ACAE1 (417 nm, 30 mw) and diode laser Sanyo DL S (785 nm, 80 mw), the η D is 0.28, 0.22 and 0.65 respectively. The third parameter that has been measured is the internal quantum efficiency of the diode laser η I. It is defined as the fraction of the injected carriers that recombine radiatively and it is given by; I T 1 = 20 o C T 2 = 29 o C Linear Fit of T= 20 o C T O = 85.5 K P v t where V is the power supply voltage. η I for diode laser Toptica Photonics DL100 is 19 %, for diode laser Nichia NDHV310ACAE1, 417 nm, 30 mw, is 15 % and for diode laser Sanyo DL S is 26 % which is calculated from slope efficiency of the experimental L. I. curve for each laser. Finally the characteristic temperature of the diode laser, T o, is calculated which is defined as a measure of the temperature sensitivity of the device and dependent on the particular diode whose value is a measure of the quality of the diode. Higher values of T o imply that the threshold current and external differential quantum efficiency of the device increase less rapidly with increasing temperatures. This means the laser being more thermally stable. Usually T o ranges from 70 K for the worst diodes to 135 K for the best ones [23]. The ratio between the threshold values at two temperatures differing by T is given by (I th1 /I th2 ) = exp ( T/T o ). The experimental work to determine the temperature characteristic of the GaN diode laser Toptica Photonic DL100 was made by measuring the light versus current (L.I.) curve of the lasers at various temperatures as shown in Fig Injected Current (ma) Fig. 4: L.I. curve at two different temperatures for diode laser Toptica, 403 nm, 30 mw. From the experimental work the T 0 for diode laser Toptica DL100 (403 nm) is equal to 85.5 K, T 0 for diode laser (6) Sanyo DL S (785 nm) is equal to 86 K and T 0 for diode laser Nichia NDHV310ACAE1 (417 nm), is equal to 137 K. These results for all diode lasers showed good agreement with theoretical values. The diode laser Nichia NDHV310ACAE1 (417 nm) resulted to be the best diode laser being less sensitive to temperature changes. Summary To summarize, diode lasers are perfectly suited for optical trapping applications thanks to their low cost, user friendly operation, long term stability in output power and frequency. Both micro and nanoparticles (nanotubes, nanowires, graphene) are routinely trapped and manipulated in our optical tweezers experiments. The sensitivity of diode lasers to optical feedback is the crucial enabling property for feedback-controlled optical trapping. The external optical feedback, when it is sufficiently strong, results in a large stability of the diode laser and it is much more easily detected than in other lasers because of the strong dependence of the refractive index of the diode laser active region on the carrier density. Such novel approach will open perspective for extending the use of light forces with low numerical aperture lenses much increasing the trapping depth, trapping efficiency and spatial range in experiments. References [1] C. J. Foot, Atomic Physics, Oxford University Press, Oxford, (2005); [2] L. Ricci, M. Weidemuller, Opt. Comm. 117(1995)541; [3] A. Ashkin, Phys. Rev. Lett. 24 (1970) 156; [4] A. Ashkin, et al. Opt. Lett. 11 (1986) 288; [5] A. Jonas, P. Zemanek, 29 (2008) 4813; [6] F. Borghese, et al. Opt. Express 15 (2007) 11984; [7] A. Ashkin, J. M. Dziedzic, T. Yamane, Nature 330 (1987) 769; [8] M. D. Wang, et al. Science 282 (1998) 902; [9] Y. Liu, et al. Biophys. J. 68 (1995) 2137; [10] D. Preece, et al. J. Opt. 13 (2011) ; [11] O. M. Maragò, et al. Nano Lett. 8 (2008) 3211; [12] O. M. Maragò, et al. Physica E 8 (2008) 2347; [13] P. H. Jones, et al. ACS Nano 3 (2009) 3077; [14] P. J. Pauzauskie, et al. Nat. Mater. 5 (2006) 97; [15] A. Irrera, et al. Nano Lett. (2011), DOI: /nl202733j; [16] A. A. R. Neves, et al., Opt. Express 18 (2010) 822; [17] O. M. Maragò, et al., ACS Nano 4 (2010) 7515; [18] R. Saija R., et al. Opt. Express 17 (2009) 10231; [19] E. Messina, et al. ACS Nano 5 (2011) 905; [20] E. Messina, et al. J. Phys. Chem C115(2011) 5115; [21] C. Ye, Tunable External Cavity Diode Laser, (2004); [22] B. Tromborg, J. H. Osmundsen, IEEE J. Quantum Electr., QE-20 (1984) 1023; [23] O. Svelto, Principles of Lasers, (1993). 84

85 INTERFERENCE WITH COUPLED MICROCAVITIES R. Stassi a, O. Di Stefano a, S. Savasta a a) Dipartimento di Fisica della Materia e Ingegneria Elettronica,Università di Messina Viale S. D Alcontres, S.Agata-Messina, Italy Abstract Here we propose an all-optical analogue of the effect of sign change under 2π rotation based on time-resolved optical interference in coupled optical microcavities. Feeding the coupled-microcavity system with a pair of phase-locked probe pulses, separated by precise delay times, provides direct information on the sign change of the transmitted field. Introduction In quantum mechanics if we want to perform a rotation of a generic quantum state, we have to apply the operator U(θ) = exp(-ij θ/2) on the corresponding ket. A rotation by 2π radiants around the z-axis, which intuitively ought to be equivalent to no rotation at all, multiplies the eigenstate of J 2 and J z by 1 if j=n/2, with n integer, and where J is the angular momentum operator. It is necessary a rotation by 4π radians to return to its initial state. As observables in quantum theory are quadratic in a wave function, the change of sign cannot be detected by ordinary experiments. The first Gedanken experiments aimed at the observation of the sign change of spinors under 2π rotations were published by Bernstein and independently by Aharonov and Susskind. These two proposed experiments, the first involving the interaction of a spin 1/2 particle with a magnetic field, and the second involving the tunneling of a current of free electrons, were conceptually similar. In both cases one system was split into two separate subsystems, one of them was affected by an additional 2π rotation relative to the other one, and then recombined. The first experimental verification of coherent spinor rotation was provided by Rauch et al. and Werner et al., both groups employed unpolarized neutron interferometry as suggested in the Bernstein-Gedanken experiment. Klein and Opat reported the observation of 2π rotations by neutron Fresnel diffraction. The similarity of the mathematical description (that is, the algebraic isomorphism) between spinor rotations and the transitions between two atomic or molecular states of any total angular momentum has been exploited to study analogies of 2π spin rotations with different experimental approaches that required no fermions. One other system, where such an effect has been observed, consists of strongly interacting Rydberg atoms and microwave photons: after a full cycle of Rabi oscillation, the atomcavity system experiences a global quantum phase shift π. We consider a system of two coupled planar microcavities (MCs). When one of the two is excited by an ultrafast resonant optical pulse, the energy oscillates between the two systems until losses through the external mirrors prevail. In such systems the coupling of the two cavity modes can be controlled by the transmission of the central mirror and the two resonant modes are the optical analogs of two atomic or molecular states, which, in turn, are isomorphic to a spin 1/2 system. We provide with this system a concrete and conceptually simple all-optical realization of the sign change under 2π rotations. Two Coupled Oscillators with source term A semiconductor planar MC is a structure formed by high reflecting dielectric mirrors [distributed Bragg reflectors (DBR)] on the two sides of a spacer (Sp) layer, of physical length L C. Here, we consider a system composed by two planar MCs connected through a common DBR (see Fig. 1). We assume that the two MCs have a high Q factor and that the intracavity modes are coupled with the external field via two partially transmitting mirrors. In the figure 2, the dashed line represents the single mode of an empty microcavity. The continuous line represents the splitting in energy of the former mode when we couple two identical microcavities. The two resonant modes are the optical analogues of two atomic or molecular states, which, in turn, are isomorphic to a spin 1/2 system. We consider systems with coupling-induced splitting quite larger than the linewidth of the individual peaks. Figure 1: Scheme of a double microcavity 85

86 Figure 2: Resonant modes of (dashed line) one empty MC and (continuous line) two coupled MCs. We consider excitation of the system by a Gaussian light pulse arriving from the left of the coupled system Figure 3: light field transmitted intensity inside the cavity in function of time when is sent a single excitation. 1 (t 2 t0 ) 0 (t t0 ) t) e e ( (1) 2 The calculated field intensity is shown Fig. 3. The figure also displays (arb. units) the corresponding Gaussian input pulse. The transmitted intensity displays a damped oscillatory time behavior (with Rabi frequency Ω R ) originating from the combination of coherent energy exchange between the two MCs and losses through the external mirrors. To inspect the phase of the transmitted field after one or two Rabi-like oscillations, we now consider a second pulse in phase with the first one sent from the left into the double semiconductor planar MCs. The total input field can be expressed as, (t 2 t1) 0 (t t1) t) 1(t) e e 1 ( (2) 2 Figure 4: transmitted intensity calculated when a second pulse is sent after one complete Rabi-like oscillation. The transmitted intensity is calculated for two different physical situations as shown in Fig. 4 and 5. First we address the case when the arrival time of the second pulse is chosen so that the corresponding first maximum in the transmitted field is exactly in time with the second maximum originating from the first pulse Fig. 4. In particular the time delay between the two pulses corresponds to a complete Rabi-like oscillation: Ω R (t 1 - t 0 )=2π. In this case we find that the total signal is strongly damped due to destructive interference. Figure 5: transmitted intensity calculated when a second pulse is sent after two complete Rabi-like oscillations. 86

87 Hence, such an abrupt damping of the signal demonstrates that the transmitted field after a complete oscillation acquires a π phase (minus sign). If the arrival time of the second pulse is chosen so that Ω R (t 1 -t 0 )=4π (see Fig. 5) the total signal gets amplified due to constructive interference. This condition is verified when the corresponding first maximum in the transmitted field is exactly in time with the next (third) maximum originating from the first pulse. Analytical Model The essential physical features of such a system may be understood through a simplified analytical model. We adopt the quasimode approach. The discrete cavity modes (one for each MC) interact with an external multimode field. The quasimode approximation allows us to describe such systems analogously to a two interacting oscillators system. In particular, we consider a system of two coupled harmonic oscillators (the light modes of the two coupled cavities) with an external source ε(t). The Hamiltonian of such a system can be written as H a a b b g( a b b a) 0 0 * ( t) a ( ) t a where a and b are, respectively, the bosonic operators relative to the single mode in each cavity, the coupling g depends on the reflectivity of the central mirror, and ε(t) describes the feeding of the cavity by a classical input beam. The resulting evolution equations for the photon operators inside the two cavities are i d i a 0 a g b dt 2 a () t i d i b 0 b g a dt 2 b where < > indicates the mean value of the operator, and γ takes into account the damping and losses of a field inside the structure and may be considered as a phenomenological parameter or as obtained from the master equation for two coupled oscillators interacting with a zero-temperature thermal reservoir. In the rotating frame (putting ω 0 = 0), if losses are neglected (γ = 0) and considering the input field in the cavity as a sharp pulse sent at t = t 0 we obtain (3) (4) a b a a 2 b b 2 A i cos A sin R R ( t t0) 2 ( t t0) 2 1 cos R( t t0) A cos R( t t0) A 2 2 where Ω R = 2g/ħ represents the Rabi frequency. We now calculate the number of photons emerging from the cavity on the right, <b b>, that can be measured by a photodetector. Inspecting the last two equations, we observe that it oscillates with a Rabi of frequency Ω R. Instead, we observe, as is evident from the first two equations, that b oscillates with a double period with respect to the light cavity population (i.e., at a frequency equal to Ω R /2). After a Rabi period T = 2π/ Ω R, we have <b> T = <b> 0 = -A/ħ. Such behavior is the optical analog of the spin-1/2 system undergoing a 2π rotation in ordinary space. In addition, if the time delay is t = 2T = 4π/R (i.e., after a 4π Rabi oscillation) then <b> T = <b> 0 = A/ħ: the two signals are now in phase and we have the corresponding 4π rotation in a spin-1/2 system. We observe no phase change behavior in <b b>. The results in this section show that the simple analytical model here analyzed contains all the essential physics of the process including the π phase shift after a complete Rabi-like oscillation. Conclusion In this paper we proposed an all-optical analog of the well-known sign change of the spinor wave functions under 2π rotations. The system here investigated consists of two planar MCs coupled through a central mirror. Here the two modes (in the absence of coupling) play the role of the two spin states, whereas the coupling induces a quasiperiodic exchange of the optical excitation among the two modes after ultrafast optical excitation. A complete oscillation of the excitation from one mode to the other and back is the optical analog of a 2π spin rotation. We showed that by feeding the coupled-mc system with a pair of phase-locked probe pulses separated by precise delay times, we can gather direct information on the sign change of the transmitted field after one complete Rabi-like oscillation period. Such results were explained qualitatively by a simplified physical model considering two coupled damped oscillators (5) 87

88 References [1] H. J. Bernstein, Phys. Rev. Lett. 18, 1102 (1967); [2] Y. Aharonov and L. Susskind, Phys. Rev. 158, 1237 (1967); [3] H. Rauch, A. Zeilinger, G. Badurek, A.Wilfing,W. Bauspiess, and U. Bonse, Phys. Lett. A 54, 425 (1975); [4] S. A.Werner, R. Colella, A.W. Overhauser, and C. F. Eagen, Phys.Rev. Lett. 35, 1053 (1975); [5] A. G. Klein and G. I. Opat, Phys. Rev. D 11, 523 (1975); Phys. Rev.Lett. 37, 238 (1976); [6] A. Abragam, The Principles of Nuclear Magnetism (Clarendon Press, Oxford, 1961); [7] E. Klempt, Phys. Rev. D 13, 3125 (1976); [8] M. P. Silverman, Eur. J. Phys. 1, 116 (1980); [9] J. M. Raimond, M. Brune, and S. Haroche, Rev. Mod. Phys. 73, 3 (2001); [10] A. Ridolfo, S. Stelitano, S. Patané, S. Savasta, and R. Girlanda, Phys. Rev. B 81, (2010); [11] M. E. Stoll, A. J. Vega, and R. W. Vaughan, Phys. Rev. A 16, 1521 (1977); [12] A. Armitage, M. S. Skolnick, V. N. Astratov, D. M. Whittaker, G Panzarini, L. C. Andreani, T. A. Fischer, J. S. Roberts, A. V. Kavokin, M. A. Kaliteevski, and M. R. Vladimirova, Phys. Rev. B 57, (1998); [13] G. Panzarini, L. C. Andreani, A. Armitage, D. Baxter, M. S.Skolnick, V. N. Astratov, J. S. Roberts, A. V. Kavokin, M. R.Vladimirova, and M. A. Kaliteevski, Phys. Rev. B 59, 5082 (1999); [14] S. Vignolini, F. Intonti, M. Zani, F. Riboli, D. S.Wiersma, L. Balet, L. H. Li, M. Francardi, A. Gerardino, A. Fiore, and M. Gurioli, Appl. Phys. Lett. 94, (2009); [15] 28P. Yeh, Amnon Yariv, and Chi-Shain Hong, J. Opt. Soc. Am. 67, 423 (1977). 88

89 SPECTRAL DEPENDENCE OF THE AMPLIFICATION FACTOR IN SURFACE ENHANCED RAMAN SCATTERING C. D Andrea a,b,*, B. Fazio a, A. Irrera a, P. Artoni c, O.M. Maragò a, G. Calogero a and P.G. Gucciardi a a) CNR Istituto Processi Chimico-Fisici, Viale F. Stagno D Alcontres, 37, I-98158, Messina, Italy b) Dottorato in Fisica dell Università di Messina, Dip.to di Fisica, F. S. D Alcontres, I S. Agata - Messina, Italy c) MATIS, CNR - Istituto per la Microelettronica e i Microsistemi, Via S. Sofia, 64, I-95123, Catania, Italy * Corresponding author, dandrea@me.cnr.it Abstract Surface Enhanced Raman Scattering (SERS) is characterized by a strong signal amplification (up to ) when both the excitation and the Raman photons frequencies match the localized plasmon resonances (LSPR) of the nanoparticles (NPs). In order to understand if the effective LSPR profile refers to the bare NPs or to the resonance of NPs dressed with the probe molecules, we perform multiwavelength (514nm, 633nm and 785nm) SERS experiments using evaporate gold NPs as SERSactive substrate on which we deposited Methylene Blue molecules (MB) that yields a resonance energy red-shift and a broadening of the LSPR profile. The SERS spectra at the investigated excitation wavelengths display a different intensity ratio of the characteristic MB band (peaks at 450 cm -1 and 1620 cm -1 ) with respect to the Raman counterpart. In presence of MB molecules, a red shift of 50 nm in the LSPR is observed The enhancement of the Raman modes at the different excitation wavelengths follows a trend similar to the LSPR profile of the dressed NPs, although the maximum enhancement is found at 785nm excitation, in spite of a LSPR peak at 600nm. Introduction Surface enhanced Raman Scattering (SERS) is an ultrasensitive spectroscopy technique that allows the detection of molecules adsorbed on noble metal nanoparticles (Au, Ag, Cu, etc) at sub-pico molar concentrations and enables to detect, under optimal condition, a single molecule [1, 2]. The giant signal amplification of SERS is related to the collective excitation of nanoparticles (NPs) conduction electrons, the so-called localized surface plasmon resonance (LSPR). When the frequency of incident photons is resonant with the LSPR of NPs, an increase of the electromagnetic (EM) fields can be obtained in the region close to the NPs surface, called Hot spots [3]. In particular, in SERS, when both the excitation and the Raman photons frequencies (ω L and ω R, respectively) are resonant with the LSPR of the NPs, the enhancement can reach order of magnitude as demonstrated experimentally [4-8] and theoretically, according to the E 4 approximation [9,10]. The LSPR profile strictly depends on the size/shape of the particles, the inter-particle distance, the surrounding medium [11,12], and the spectral dependence of both the excitation field enhancement factor A exc (ω) and the reradiation enhancement factor A rad (ω) have been observed to be proportional to the LSPR profile, Q(ω) [4, 12]. The spectral dependence of Q(ω) is therefore particularly important since it determines both the best excitation wavelength for optimal SERS detection and the reradiation enhancement of the Raman modes. It is still not known, however, whether the effective Q(ω) refers to the LSPR of the bare NPs or to the resonance of the NPs dressed with the probe molecules [Q dress (ω)]. The latter is typically energy shifted and can be much broader, according to the molecular dielectric constant. The LSPR profiles can be obtained easily by extinction spectroscopy, which is the easiest and most powerful tool to study the resonance energy of metal NPs. Differently from the extinction spectroscopy that is a far-field technique, SERS measurements give insight on the local near-field (the field in the hot spots) so, detailed comparison of the SERS enhancement factor (EF) with the LSPR profiles of SERS-active substrates is a possible way to understand the properties of the electromagnetic hot spots in NPs. To get insight on this phenomenon we carried out multi-wavelength SERS experiments using evaporated gold nanoparticles as SERS-active substrates on which we deposited Methylene Blue molecules that notably alter the LSPR profile. The SERS peaks intensities, normalized to the Raman intensities measured on a flat gold region, and the relative enhancement factor of the Methylene Blue Raman modes were compared with the LSPR spectra highlighting an additional frequency shift, not appreciable in the LSPR profile. Materials and methods The gold clusters were prepared by Electron Beam Evaporation (EBE) on SiO 2.The sample was heated at 480 C and a gold amount of cm -2 was evaporated. 89

90 Figure 3: Extinction spectra of bare Gold Nanoparticles (black line) and after (blue line) the binding of the Methylene Blue molecules. The three colour line and box indicate the excitation line and the corresponding Raman region of MB for the three lasers of our apparatus. Gold atoms arrive on the heated substrate, so they have the possibility to diffuse over the substrate, immediately starting a ripening process leading to cluster formation. In order to promote the adhesion of the gold NPs to the substrate, the clusters were covered by a thin Silicon Oxide layer (2-3 nm) produced by RF magnetron sputtering. The Methylene Blue (MB) solution was prepared mixing deionized water with the powder (Carlo Erba Reagenti) at the concentration of 10-4 M. The samples of gold NPs were soaked into aqueous solution of dye for 1h, then washed in water and dried in vertical position to avoid formation of too thick multilayer of molecules on substrates. This method guarantees that only a single layer of MB dye remains adsorbed onto the array, as reported in literature [3,7,13]. Extinction and SERS experiments were carried out with a HR800 Jobin Yvon microspectrometer. For the extinction measurements, we exploiting the white light xenon lamp embedded in the microscope of the HR800 spectrometer. A 10X objective was used to collect the light transmitted through the sample and the HR spectrometer was used to acquire the optical signal. The LSPR profile was then proportional to the ratio between the light transmitted in absence (I0) or in presence of NPs (INPs). For multi-wavelength SERS measurements we coupled our spectrometer with an Ar++ (515 nm), a He-Ne (633 nm) and a diode (785 nm) laser. In this back-scattering Raman setup, measurements were done focusing a few tens of µw of laser power on a submicron spot using a 100X microscope objective (NA 0.95). All the spectra were acquired with integration times from 10 to 120 seconds and power over the range from 4 to 400μW. Discussion Figure 1 shows the different LSPR profiles between the bare NPs (blue line) and dressed NPs (black line). The presence of a layer of Methylene Blue molecules bound to the gold NPs substrate yields a resonance energy red-shift of about 50 nm (from 570 nm to 620 nm) and a broadening of 50 nm. By using the several excitation wavelengths available in the experimental set up, we were able to excite the ascending and the descending region of the dressed LSPR profile Q dress (ω) (with 515 nm and 633 nm laser lines), and the out of resonance region (by using the laser line at 785nm), where we don t expect SERS effect (colour lines in Fig. 1). As shown in figure 1 by the colour boxes relative to each excitation wavelength, the Raman spectrum of MB extends in the cm -1 region [7, 13] with the most intense peaks at 450 cm -1 and 1620 cm -1. According to previous study [14], looking the extinction profile, for the laser excitation at 515 nm we can expect a progressive increase of the intensity of the SERS Raman mode of MB passing from the low frequencies to the higher, with respect to the Raman mode in absence of SERS effect. An opposite behaviour is envisaged for the laser excitation at 633 nm; in this condition the 450 cm -1 bands are closer to the LSPR peak, and then to the condition of maximum resonance. The SERS spectra at the investigated excitation wavelengths (fig. 2, colour lines) display, as expected, a different intensity ratio of the 450 cm -1 and 1620 cm -1 peaks with respect to the Raman counterpart. For each excitation wavelength, in fact, to comparing SERS and Raman spectra and to calculate the EF, we acquired the MB Raman modes coming from a flat gold region (fig 2, black lines). This expedient allowed us, also, to exclude any contributions linked to chemical bonds between gold and Methylene blue. Figure 4: SERS spectra of Methylene blue for 515, 633 and 785 nm excitation wavelength (colour line) compared with the Raman counterpart acquired on a flat gold region (black line). 90

91 At 515 nm (green line) the 1620 cm -1 mode is more enhanced with respect to the peak at 450 cm -1, but a similar trend is also observed for excitation wavelength at 633 nm (red line). This behaviour is not compatible with the both the LSPR profiles acquired in the extinction measurements. This trend is extended until the near infrared region by using an excitation wavelength of 785 nm; here the SERS spectra show a higher enhancement of the modes at 450 cm -1 than those at 1620 cm -1. Comparing the intensity of the principal bands of Methylene Blue SERS spectra with the corresponding Raman modes, it was possible to plot the relative mode enhancement factor versus the Raman shift for each excitation wavelength, as showed in figure 3. In this picture is evident the incremental behaviour of the EF for the visible excitations: at 515 nm we have an enhancement from 8 times for the low frequency modes, to 30 for the bands at 1620cm -1. In the same way, at 633 nm (central box) the modes experience an EF from 220 to 350 times. explanation in agreement with the experimental data that can be used for a quantitative prediction of the shift. This work is a partial study, contribute for the PhD annual report, but it opens the way for future measurements and considerations. Our purpose is to extend the number of excitation wavelength. Using 532, 560, 660 and 695 nm excitation sources we can complete our multi-wavelength analysis and try to find the exact position of the maximum EF, since to obtain a complete profile to compare with the LSPR profile. At the same time, this experimental data may be of interest for theoretical calculations in order to clarify the connection between the far-field and the near-field point of view of the same effect. Conclusion Multi-wavelength SERS measurements were carried out on SERS active substrates of gold evaporated nanoclusters. The SERS intensities of the modes of the probe molecules, the Methylene Blue, were studied and compared with the corresponding Raman spectra. Then, the SERS Enhancement Factor behaviour was compared with the Local Surface Plasmon Resonance profile of the substrate. The presence of Methylene blue soaked on gold nanoparticles causes an energy red shift and a broadening of LSPR profile, as known in literature, but the maximum enhancement was obtained for an excitation wavelength in the Near Infrared region (785nm), in spite of LSPR peak at 600 nm. These results open the way for further measurements and calculations for a better understanding about the differences between near and far field point of view, basics for a proper comparison between the LSPR and SERS profiles, and thus for the optimization of the enhancement factors. Figure 5: Relative SERS enhancement factor for the 515, 633 and 785nm excitation wavelengths. The colour lines are guide for eyes. The maximum EF was obtained for the excitation at 785 nm, and joining 4 orders of magnitude for the bands at 450 cm -1, and decreasing of a factor of 10 (until 3 orders of magnitude) for the higher frequency modes. Thank to the colour lines, guide for eyes, is evident the new behaviour extrapolated by the SERS spectra: the maximum enhancement happens for visible-nir region, 100 nm red shifted with respect to the peak of the LSPR profile. The red shift of the near-field peak energies with respect to the far-field quantities is a well-known phenomenon in literature. It depends to the size of the particles, with larger particles displaying a more marked shift [15], but there is not a complete and simple Acknowledgments We acknowledge funding from the EU-FP7- NANOANTENNA project GA Development of a high sensitive and specific nanobiosensor based on surface enhanced vibrational spectroscopy and the PRIN 2008 project 2008J858Y7_004 Plasmonics in selfassembled nanoparticles / Surface Enhanced Raman Spectroscopy on self-assembled metallic nanoparticles. References [1] S. Nie and S. R. Emory, Science 275 (1997) 1102; [2] K. Kneipp et al., Chemical Physics 247 (1999) 155; [3] G. Laurent et al., Physical Review B 71 (2005) ; [4] E.C. Le Ru et al. Journal of Physical Chemistry C 112 (2008) 8117; 91

92 [5] H. Wang et al., Journal of American Chemical Society 127 (2005) 14992; [6] E.C. Le Ru et al., Journal of Physical Chemistry C 111 (2007) 13794; [7] G. Xiao and S. Man, Chemical Physics Letters 447 (2007) 305; [8] M. Kall et al., Journal of Raman Spectroscopy 36 (2005) 510; [9] K. Kneipp et al., Chemical Review 99 (1999) 2957; [10] E.C. Le Ru et al., Chemical Physics Letters 423 (2006) 63; [11] A. Otto, Journal of Raman Spectroscopy 22 (1991) 743; [12] E.C. Le Ru et al., Current Applied Physics 8 (2008) 467; [13] S. Nicolai and J. Rubim, Langmiur 19 (2003) 4291; [14] A. McFarland et al., Journal of Physical Chemistry B 109 (2005) 11279; [15] J. Zuloaga and P. Nordlander, Nanoletters 11 (2011)

93 PHOTOLUMINESCENCE OF A QUANTUM EMITTER IN THE CENTER OF A DIMER NANOANTENNA: TRANSITION FROM THE PURCELL EFFECT TO NANOPOLARITONS N.Fina a, *, A.Ridolfo b, O.Di Stefano a,, O.M.Maragò c,s.savasta a a)dipartimento di Fisica della Materia ed Ingegneria Elettronica,Università di Messina, Viale F.S. D Alcontres 31, 98166, Messina, Italy b) Technische Universitat Munchen, Physik Department, Germany. c) Istituto per i Processi Chimico-Fisici, Viale F. Stagno d Alcontres 37, 98158, Messina, Italy * Corresponding author, nfina@unime.it Abstract We present a fully quantum mechanical approach to describe the light emitting properties of strongly interacting plasmons and excitons. Specifically we present calculations for ultracompact quantum systems constituted by a single quantum emitter (QE) (a semiconductor quantum dot) placed in the gap between two metallic nanoparticles. Light emitted by the quantum dot is shown to undergo dramatic intensity and spectral changes when the emitter excitation level is tuned across the gap-plasmon resonance. The resulting plexciton dispersion curve differs significantly from the one obtained via scattering experiments [1]. Our work suggests that the strong interaction between metallic nanoparticles and excitons can exploited for tailoring the spectral properties of quantum emitters for the realization of ultracompact colored and white LEDs. Introduction The light-matter strong coupling regime is fascinating, as it allows nonlinear quantum optics experiments to be done with as few as two photons, control of the direction of emission or phase of one photon with another one, the observation of single-atom lasing, the study and exploitation of quantum entanglement [2]. Here we investigate the emission properties of two Silver Metal Nanoparticles (MNP) with a Quantum Dot (QD) between these (see Fig. 1). In particular we study the modifications of the quantum emitter photoluminescence (PL) induced by the presence of the metallic nanoparticles (MNPs). We also study the transition from the weak to the strong coupling regime. Fig.1 Dimer nanoantenna with quantum emitter. Entire system is embedded in an optically active medium. Theory The system is schematically showed in Fig1. It is entirely embedded in a medium with constant permittivity ε. The expectation value of the total system polarization b is given by: Pm f a (1) where a is the destruction operator for the localized surface SP mode, the QD dipole moment e d, and the coefficient f is given in Eq. (10). The term operator is the expectation value of the lowering transition g e. The QE and the MNP interacts via dipole-dipole coupling. States g e transition is resonantly coupled with the localized surface plasmon dipole mode with a strength g, as showed in Fig 2. 93

94 Where: H i a a g (5) int ( ) g (6) being 4 6 ' (8Q 1) r 0 3 (7) a field term related to the whole system, and, where: 3 R Q (8) S r 3 Fig 2. Quantum emitter two level representation: external optical pump excites ground QD states, giving rise to excitonic emission of light caused by interaction with MNPs-SP. Electrons are optically or electrically pumped from lower levels j to upper levels i, then decay nonradiatively to level e. Electrons finally decay by spontaneous emission to level e.the full quantum dynamics of the coupled nanosystem can be derived from the following master equation for the density operator, i(, HS ) LX L sp (2) Where H S represents the Hamiltonian terms including free dynamics, interaction and driving, i.e.: with HS H0 Hint H drive (3) H0 spa a x (4) where x and sp are the energies of the QD excitonic and MNP plasmonic transitions. Eq.(4) represents the free system Hamiltonian equal to the sum of free MNP system term with free QE term. The Hamiltonian term describing the interaction between the QD exciton and the quantized SP field, in the rotating wave approximation reads: with S 1, 2, whether the field polarization is parallel or orthogonal to the R direction [3], while ' is a parameter depending on SP resonance frequency. The system excitation by a classical input field can be described by: H E ( a a) E ( ) (9) * drive 0 0 Notice that E 0 is different from zero only in scattering calculations. The Markovian interaction with reservoirs determining the decay rates γ and γ for the QD exciton and the SP mode respectively, as well as the pumping mechanism of the QD, is described by the Liouvillian terms, L and L [4]. Furthermore we X found that the term related to interaction of MNPs-SP with incoming field is f, and it s given by: Results f 48iQ b 2 (1 8 Q) 3 x sp ' r 3 0 sp (10) We have calculated the PL on a system with a 6nm radius MNP at a distance R = 9.5 nm embedded in a medium with a dielectric constant ε b = 3. 94

95 Fig.3 : Calculated dimer nanoantenna-qe PL spectrum for different dipole moments. In Fig.3 we can see how, on increasing the QD dipole moment, the splitting between the two PL peaks enhances [5]. This is due to the fact that the Vacuum Rabi Splitting (VRS) limit is given by the following condition: 2 (γ +γ ) x sp g (11) 2 and, because, from Eq.(6), g is related to dipole moment, on increasing of it, will increase the VRS, as shown by PL spectra. The PL spectra achieved at different distances between the two MNPs, tuning the exciton frequency on the resonance MNP-SP frequency, with a dipole moment μ/e =0.7nm, are shown in Fig.4. We can see how, on increasing the distance QE-MNP, strong coupling plexcitonic effect, progressively, vanishes, until to show only the QD dipole row (on R=28nm). Fig.4 : PL spectra calculated for different distances centered at frequency a. On increasing distances the double peak splitting disappears. A dipole moment μ/e =0.7nm has been used. The influence of MNPs on the PL of quantum emitter has been studied in the weak coupling regime [7]. Here we addressed the situation where the interaction between the emitter(s) and the MNPs is so strong that a perturbative approach fails. Figure 5 displays a series of PL spectra taken at different exciton-sp energy detuning. The typical anticrossing behavior, characteristic of the strong coupling regime, can be observed. At large detunings the PL emission is concentrated at the transition energy of the emitter. 95

96 Conclusions We have investigated for the first time light emission properties of QEs strongly coupled to MNPs. When strong coupling is achieved, light emitted by the QD is shown to undergo dramatic intensity and spectral changes when the emitter excitation level is tuned across the gapplasmon resonance. The resulting plexciton dispersion curve differs significantly from the one obtained via scattering experiments. This work suggests that the strong interaction between metallic nanoparticles and excitons can exploited for tailoring the spectral properties of quantum emitters for the realization of ultracompact colored and white LEDs. Fig.5. PL spectra taken at different exciton-sp energy detuning. When the transition energy approaches the SP resonance, two emission peaks are clearly visible and emission is shared by the two polariton modes. For comparison, Fig. 6 shows scattering spectra [6] which display a different behavior and a different normal mode splitting. References [1] A. Ridolfo et al., Phys. Rev. Lett. 105, (2010); [2] Kimble, H. J. Strong interactions of single atoms and photons in cavity QED. Phys. Scripta 76, (1998); [3] S.A Maier Plasmonics: Fundamentals and applications, Springer; [4] M.O. Scully, M.S. Zubairy, Quantum Optics, Cambridge Univ.press; [5] G.Khitrova et al. Nature Physics 2, (2006); [6] S.Savasta et al., ACS Nano 4 (11)(2010), pp [7] L.Novotny,B.Hecht, Principles of Nano-Optics, Cambridge Univ.pres Fig.6. Scattering spectra as a function of the exciton resonance. 96

97 LATERAL DIFFUSION OF DPPC AND OCTANOL IN A LIPID BILAYER MEASURED BY PFGE NMR SPECTROSCOPY S. Rifici a, * a)dottorato in Fisica dell Università di Messina, Dip.to di Fisica, F.S. D Alcontres,98166 S. Agata-Messina, Italy * Corresponding author, srifici@unime.it Abstract Lipid lateral diffusion coefficients in the system of 1,2- palmitoyl-sn-glycero-3-phosphocholine (DPPC), Octanol and water were determined by the pulsed field gradient NMR technique on macroscopically aligned bilayers. The molar ratios between DPPC and Octanol and between DPPC and water were set to 1:2 and 1:28 respectively. The temperature was varied between 270 K and 323 K. Introduction Cell membrane is the first part of the cell to be in contact with any nutrient or pathogen in the extracellular matrix. Biological membranes are complex mixtures of different lipid molecules and proteins. A lipid is an amphiphilic molecule with an hydrophilic polar headgroup and usually two hydrophobic hydrocarbon chains. When dispersed in an aqueous environment, lipids self-assemble in order to reduce contacts with water. They can arrange themselves in a variety of morphologies depending on the structure of the lipid, the nature of the lipid headgroup and its degree of hydration, temperature, concentration and osmotic pressure. Multilamellar vesicles, continuous ordered bilayers and monolayers, liposomes and micelles are typical examples of possible structural arrangements. [1] Single artificial phospholipid, or simple mixtures of artificial phospholipids have long been used as mimetic membranes for examining the physical, chemical and biological properties of the biomembranes. This approach is justified by the observation that some model membrane systems have been widely recognized as essentially equivalent to natural systems such as those found in myelin and erythrocyte membranes. [2] Dipalmitoylphosphatidylcholine (DPPC) has a very simple chemical structure, a phosphocoline (PC) headgroup and two identical linear saturated hydrocarbon chains, and plasma membrane contains a relatively large amount of phospholipids with PC headgroup, this is why DPPC is so largely used in all studies about model membrane. Despite it has been widely studied, his dynamics are still not well understood. Many structural and dynamic intrinsic properties of aqueous dispersions of lipid bilayers are governed by temperature. In the case of phosphatidylcholines, these phase transitions take place within the temperature range K, depending on the strength of the attractive Van der Waals interactions between adjacent lipid molecules. Longer tailed lipids have more area to interact, increasing the strength of this interaction and consequently decreasing the lipid mobility. Transition temperature can also be affected by the degree of unsaturation of the lipid tails. An unsaturated double bond can produce a kink in the alkane chain, disrupting the lipid packing. This disruption creates extra free space within the bilayer which allows additional flexibility in the adjacent chains. [3] DPPC shows three kinds of structural changes with increasing temperature under atmospheric pressure. This changes are thermotropic phase transitions: the subtransition from the lamellar crystal (Lc) phase to the lamellar gel (Lβ ) phase, the pre-transition from the Lβ phase to the ripple gel (Pβ ) phase, and the main transition from the Pβ phase to the liquid crystalline (Lα) phase occur in turn with increasing temperature. [4] The (Lα) phase is considered the most important, because many biologically relevant processes occur in this phase. Indeed, lamellar bilayers in the fluid phase supply an efficient, planar permeability barrier, which still allows functional flexibility and lateral diffusion motions of associated membrane proteins. Adsorption of alcohol molecules or other small amphiphilic molecules in the cell membrane has a destabilizing effect on its structure. Experiments on phospholipid membranes have shown that alcohol molecules can induce the interdigitated phase [5] that, at high alcohol concentrations, replaces the ripple gel phase [6,7]. A complete interdigitation is expected at alcohol concentrations above a threshold value assumed to be about 2:1 alcohol to lipid ratio in the membranes as it has been observed for DPPC/n-butanol system by a DSC study [7]. When the interdigitation occurs, lipid molecules from opposing monolayers interpenetrating, thereby decreasing the bilayer thickness. The increase of the polar headgroup area, due to the addition of alcohol molecules, gives rise to a reduction of the Van der Waals attraction between lipid acyl chains. Bound alcohol molecules reduce the mobility of the polar headgroups and, at the same time, cause a decrease of the ordering and an additional coiling of the melted acyl chains. Concerning dynamics, different types of motions, with correlation times ranging from picoseconds (corresponding to the motion of lipid chain defects, for example) to microseconds (corresponding to collective excitations of the bilayer membrane), characterize 97

98 bilayers, a large variety of which is essential for the functionality of membranes [8,9,10]. Motions within the bilayer plane have been largely studied by NMR relaxation techniques [11,12,13] and neutron scattering [8,9,10]. Experimental details - Sample preparation The phospholipid 1,2-palmitoyl-sn-glycero-3- phosphocholine (DPPC) was purchased from Avanti Polar Lipids, Octanol was purchased from Sigma Chem. Co. Both chemicals were used without further purification. Aligned multilayers of DPPC with Octanol were obtained following the preparation suggested by Hallock [14], using mica plates as supporting substrate. Mica substrate was covered with about 1.5 mg of lipids per cm 2. Following the cited procedure, DPPC and Octanol were dissolved in an excess of 2:1 CHCl 3 /CH 3 OH (chloroform/methanol). The solution was spread and dried on the face of the substrate plate. All procedures for sample preparation were executed in a glove box under nitrogen gas to prevent lipid oxidation. This procedure resulted in a thin film covering the whole area of the mica plate. The sample was indirectly hydrated at 323 K in 96% relative humidity using a saturated potassium sulfate D 2 O solution for 12 days, after which 28 mole of D 2 O per mole of lipid were added. The mica plate was then placed in a glass tube in the diffusion probe. Nuclear magnetic resonance Self diffusion coefficients of hydration water ( D ), DPPC ( D ) and Octanol ( D Oc W ) molecules were measured by hydrogen pulsed-field gradient spin echo NMR ( 1 H-PGSE-NMR), which enables the non-invasive measurement of molecular self diffusion coefficient over a wide range of time scales (from milliseconds to seconds) directly [15, 16]. PGSE experiments were performed on aligned pure DPPC and DPPC with Octanol membranes deposited on mica sheets. All measurements were carried out in fully hydration condition at temperatures below, near and above the phase transition temperature using a Bruker AVANCE NMR spectrometer operating at 700MHz 1 H- resonance frequency. The temperature was controlled within ± 0.5 K by a heated air stream passing the sample. Self-diffusion measurements are based on NMR pulse sequences, which generate a spin-echo of the magnetization of the resonant nuclei. The method is based on sensitising the sample to molecular translational displacement by the application of magnetic fieldgradient pulses. By the appropriate addition of two pulsed-field gradients, in the defocusing and refocusing period of the sequence, of duration δ and intensity g, separated by a time interval Δ, the spin-echo intensity becomes sensitive to the translational motion along the gradient direction for the tagged molecules. These gradients, in fact, cause the nuclear spins in different local positions in the sample to precess at different Larmor frequencies, thereby enhancing the dephasing process. If the spins maintain their positions throughout the experiment, they will still refocus completely into a spin echo by the SE pulse sequence. On the other hand, if they change their positions during the experiment, their precession rates will also change, and the refocusing will be incomplete, resulting in a decrease in the intensity of the spin echo. The spin echo M(δg,Δ), is attenuated according to M M DQ (1) 2 / 0 exp[ ] where Q g and γ is the gyromagnetic ratio of 1 H. Q has the dimension of an inverse length, being a measure of the spatial scale probed, and is equivalent to the exchanged wave vector in a scattering experiment. In our experiment, the mica plate with deposited DPPC with Octanol is placed parallel to the magnetic field to test for lateral (in-plane) diffusion. To record the decay of the 1 H components, a train of pulses at increasing gradient strength is used. Integration of spectral peaks was performed using the Bruker-supplied XWIN-NMR software. Figure 1 shows the decay of spin-echo intensities for water and phospholipid/alcohol system as a function of Q 2 Δ for three different temperatures, T=287K (triangle), T=291K (circle) and T=295K (square). In the same figures, the fitting curves (continuous lines), obtained from a nonlinear fit of the Fourier-transformed peak amplitudes according to the Equation (1), are also shown. The data were fitted to an equation with three diffusion coefficients. This would be the case for a system consisting of three separated species. In fact, three decay times are clearly visible, the faster due to water molecules, the lower to phospholipid molecules, and the intermediate ascribed to Octanol molecules. The found diffusion coefficients for D, D and are reported in Table 1. D 2 W m / s 10 Table 1 W D Oc T=287K T=291K T=295K D 2 Oc m / s D m 2 / s

99 D (m 2 /sec) Activity Report 2011 Dottorato di Ricerca in Fisica, Università di Messina 1 T=287 K T=291 K T=295 K Fit 1.2x x10-9 D W D Oc D 8.0x10-10 M / M DPPC+Octanol 6.0x x x E8 1E9 1E10 1E11 Q 2 Delta [m 2 sec] Figura 1: PGSE intensity decay in fully hydrated DPPC/Octanol bilayer at T=287K (triangle), T=291K (circle) and T=295K (square). The continuous lines are the fitting functions T(K) Figura 2: The three self diffusion coefficients of hydration water (circles), DPPC (stars) and Octanol (triangles) as a function of T are shown. The self diffusion coefficient of bulk water (empty circles) in also plotted. In the case of water molecules, we found diffusion coefficients in good agreement with those measured in PC-water systems, which are in the range of m / s to m / s depending on water concentration, temperature, and bilayer composition. [17, 18,19,20,21,22]. Figure 2 shows the three diffusion coefficients as a function of T. It can be observed that the lateral diffusion coefficient increases with increasing temperature; i.e. when the full system is clearly in the liquid crystalline phase, where enhanced dynamics of the acyl chains are expected. Water and alcohol molecules follow membrane transition. Alcohol diffusion sharply lowers near the main transition temperature, and, below the transition, it seems that alcohol and DPPC molecules have the same diffusion coefficient. Below the transition, Octanol and DPPC move together, and this is an evidence of the formation of the interdigitated phase. Conclusions 1 H-PGSE-NMR experiments provided information on long-range lateral diffusion, up to some mm distances, of inter-layer water, lipid and Octanol molecules. Three decay times are clearly visible, the faster due to water molecules, the lower to phospholipid molecules, and the intermediate ascribed to Octanol molecules. In the case of water, a reduction in the diffusion coefficient alone is observed and assigned to restricted geometry. On the other hand, the phospholipid component shows a novel and interesting result of a nearly constant diffusion coefficient in the gel phase and a net increase in mobility in the liquid crystalline phase. Below the transition, Octanol and DPPC move together, and this is an evidence of the formation of the interdigitated phase. References [1] R. Lipowsky and E. Sackmann, Handbook of Biological Physics, Vol. 1, Elsevier Science, Amsterdam, 1995; [2] Rosser, M. F. N., H. M. Lu, and P. Dea. 1999, Biophys. Chem. 81:33 44; [3] R. Koyonova and M. Caffrey, Biochim. Biophys. Acta 1376 (1998) p.91; [4] N Tamai, M Goto, H Matsuki, S Kaneshina, Journal of Physics: Conference Series 215 (2010) doi: / /215/1/012161; [5] J. L. Slater and C. H. Huang, Prog. Lipid Res. 27, (1988); [6] E. S. Rowe, T.A. Cutrera, Biochemestry 29, (1990); [7] F. Zhang and E. S. Rowe, Biochemistry 31, (1992); [8] M.C. Rheinstadter, T. Seyde, L. Demmel et al., Phys. Rev. E 71 (2005) p ; [9] M.C. Rheinstadter, C. Ollinger, G. Fragneto et al., Phys. Rev. Lett. 93 (2004) p ; [10] S. Konig, W. Pfeiffer, T. Bayerl et al., J. Phys. II (1992) p.1589; [11] S. Konig, T.M. Bayerl, G. Coddens et al., Biophys. J. 68 (1995) p.1871; [12] G. Oradd and G. Lindblom, Biophys. J. 87 (2004) p.980; [13] P. Meier, E. Ohmes and G. Kothe, J. Chem. Phys. 85 (1986) p.3598; [14] Hallock K J, Henzler Wildman K, Lee D K and Ramamoorthy A 2002 Biophys. J ; [15] E.O. Stejskal and J.E.Tanner, J. Chem. Phys. 42 (1965) p.288; [16] H.V. As and P. Lens, J. Ind. Microbiol. Biotech. 26 (2001) p.43; [17] Lange, Y., and C. M. Gary Bobo. 1974, J. Gen. Physiol. 63: ; [18] Inglefield. P. T., K. A. Lindblom, and A. M. Gottlieb. 1976, Biochim. Biophys. Acta. 419: ; [19] Lindblom, G., H. Wennerstrom, and G. Arvidson. 1977, J. Quant. Chem. 12(2): ; [20] Chan, W. K., and P. S. Pershan. 1978, Biophys. J. 23: ; [21] Konig, S., E. Sackmann, D. Richter, R. Zorn, C. Carlile, and T. M. Bayerl. 1994, J. Chem. Phys. 100: ; [22] Volke, F., S. Eisenblatter, J. Galle, and G. Klose. 1994, Chem. Phys. Lipids. 70:

100 100

101 CHEMICAL EQUILIBRATION OF THE QUARK GLUON PLASMA F.Scardina a,b, *, M.Colonna b, V.Greco,b,c, M.Di Toro b a)dottorato in Fisica dell Università di Messina, Dip.to di Fisica, F.S. D Alcontres,9816 S. Agata-Messina, Italy b) INFN Laboratori Nazionali del Sud, Via S. Sofia 62, I Catania, Italy c) Dipatimento di Fisica e Astronomia, Università di Catania, Via S. Sofia 64, I Catania, Italy * Corresponding author, scardinaf@lns.infn.it Abstract The ultra-relativistic heavy ion collisions performed at the Relativistic Heavy Ion Collider (RHIC) and at Large Hadron Collider (LHC) represent the fundamental tool to study the properties of the Quark Gluon Plasma (QGP). We have studied the evolution of the QGP created in such collisions using a relativistic transport code which is based on the solution of the relativistic Boltzmann equation including elastic and inelastic two body collisions between partons. We have focused our attention on the chemical equilibration of the QGP. In fact such equilibration is a fundamental step to deal with before to analyze hadronization. We have performed calculation in a box at equilibrium in order to check the code and finally we have performed simulation for the collision in both RHIC and LHC case. The purpose of our work is to show how the QGP, which is initially composed for mostly by gluons, go towards chemical equilibrium with a consequent enhancement of the quarks number. Moreover we have studied the dependence of the chemical equilibration from the transverse momentum p T. We have observed that at the end of the evolution of the fireball the ratio Nq/Ng in the region of low p T reach the equilibrium value of The presence of a such large amount of quarks should modify the background for the various energy loss scenarios. The ratio between the quark number and the gluon number in the region of high p T do not reach the equilibrium value but is significantly different from the initial value. This difference should explain the relative abundances of the hadrons that coming from the fragmentation of high p T partons. INTRODUCTION We have studied the evolution of the QGP created in ultra-relativistic heavy-ion collision with a relativistic transport code based on the numerical solution of the relativistic Boltzmann. Using such code we have studied the chemical equilibration of the QGP created at RHIC and at LHC. The analysis of such equilibration assume a fundamental importance in order to have a comprehension of the abundances of the different species of hadrons revealed in the experiment. Moreover we want to improve the description of the QGP using an effective kinetic theory for a quasi-particle model. In such model the particle acquire an effective mass and this causes a further enhancement of the quark number. TRASPORT APPROACH We have studied the evolution of the Quark Gluon Plasma using a relativistic transport simulations based on the solution of the Boltzamann equation. p f ( x, p) C (1) Where f(x,p) are the partons distributions functions and C 22 is the collision term. C E1 (2 ) 2E2 d p d p (2 ) 2 (2 ) 2 3 ' 3 ' ' 3 ' E1 E2 ' ' d p 22 ( f f f f ) ' ' M (2 ) ( p p p p ) 4 4 ' ' υ is set equal to 2 if 1 and 2 are identical particles. For the implementation of the collision integral we use the so called stochastic algorithm[1,2]. In such algorithm if the collision will happen or not is sampled stochastically comparing the probability of the two body collision with a random number between 0 and 1. N t N N x 2 2 coll 22 vrel P If the extracted number is less than the probability the collision will occur. In the limit Δt ->0 Δx->0 the numerical solutions using the stochastic method converge To the exact solution of the Boltzamann equation. So it is important to divide the space into sufficient small cells. We consider both elastic and inelastic collision using the differential cross section indicated in the following formulas [1,3] d 2 dq q q gg gg 2 s T ( T D) (2) (3) (4) 101

102 d gg qq 2 s T T q dq 3 s( q m ) (5) over the average longitudinal momentum squared. The initial conditions in this case are set to be the same as in fig 1. d 64 dq 27 s( q m ) gg qq 2 s T T q (6) Where q T is the transverse component of moment transfer, m D and m q denote respectively the Debye mass for gluons q and quarks respectively. Calculations In a Box at equilibrium With the purpose of demonstrate the correct operation of our code we have chosen some situation in which the outcome are known analytically. Hence we have performed box calculations" in which a particle ensemble is enclosed in a box, with fixed limits, and evolve dynamically until an appropriate final time. Initially particles are distributed homogeneously within the box and their momentum is chosen highly anisotropic dn Ndp dp T z ( p 6 GeV ) ( p ) T z (7) Figure 1:Temporal evolution of energy distribution of a system consisting of N=2000 massless particle in a fixed box whose size are 125 fm 3 After a sufficiently long time the system equilibrate as shown in fig. 1. For a classical, ultrarelativistic ideal gas the energy distribution has the Boltzmann form dn NE de 1 2T 2 3 e ET / (8) In figure 1 the time evolution of the energy distribution for such box calculations is depicted the size of the box is 125 fm 3. We have considered anisotropic calculations and we have taken a constant cross section of mb. The final time is 3 fm/c. Moreover in order to improve statistics we have used 50 test particles for one real. The dotted line in the figures indicate the analytical distribution with temperature T=2 GeV calculated using The following formula 3 T (9) Where the energy density and the particle densities are given by the initial conditions. We see a good agreement between the numerical results and the analytical distributions. As we can observe from the figure our code reproduce analytical results. In order to have sufficient argument to guarantee whether our algorithm operating correctly is necessary to check other quantity, as for example the time evolution of momentum anisotropy shown in fig. 2 and defined as the average transverse momentum squared Figure 2: Time evolution of the momentum anysotopy from box calculations. The initial conditions are set to be the same as in Fig. 1 Once we have checked that our algorithm reproduce the analytical calculation relatives to kinetic equilibrium we have checked that also the chemical equilibrium of the plasma can be reproduced by our algorithm. For massless case the ratio between the number of quark and the number of gluon is simply given by the ratio between the respective degrees of freedom υ N N q g q g (10) 102

103 where υ q =2*3*N f υ g = 2*8. In our case we consider two flavour and thus the ratio between the number of quark and the number of gluons is The results are shown in fig.3 EFFECT OF THE MEAN FIELD We have the intention to introduce in our code the effect of the mean field using a quasi-particle model [4]. In such a model the interaction is encoded in the quasi particle masses and once the interaction is accounted for in this way the quasi particle behave like a free gas of massive constituents. The effect of the masses on the chemical equilibration of the plasma is substantial. In the massive case the ratio N q /N g depends on the temperature as can be calculated in the following formula N N q g q g mq / T mg / T d d q g 2 q 2 g m T m T q g 2 2 e e T T (11) Figure 3:Time evolution of the gluon and quark number in box calculations. We have considered gluons and quarks with three flavour as parton species Results for the heavy Ion collision We have performed simulations for heavy-ion collisions for both RHIC (200 AGeV) and LHC (5.5 ATeV). In figure 4 are shown the ratio between the number of quark and the number of gluons as a function of transverse momentum. The dot line indicate the initial ratio while the thick line and the dashed line indicate the final ratio obtained at RHIC and LHC respectively. We can observe that for both RHIC and LHC at low transverse momenta the ratio is near to the equilibrium value. Moreover at LHC where the evolution time is longer also at high p T the ratio is different from the initial one Where 1 1 m p ; m p T T q q g g (12) The expected ratio is indicated in fig. 5. In this figure we can observe that the value of the ratio is strongly dependent from temperature and that at the freeze-out temperature the ratio reach the value of 6.3 that is larger that the value obtained in the massless case. Figure 5: ratio N q /N g as a function of temperature calculated using the formula 0.8 Figure 4: Ratio between the quarks number and the gluon number as a function of p T Conclusions The Quark Gluon Plasma created in heavy-ion collisions seem to reach chemical equilibrium at low transverse momentum, but in the case of LHC also at high p T the ratio is significantly different from the initial one. Thus at the end of its evolution the number 103

104 of quark in the plasma is greater than the number of gluons and this have two important implication: first of all the background of the energy loss process is significantly modified and moreover the abundances of the different species (pion, proton, kaon) coming from the fragmentation of quarks and gluons are significantly affected by the increasing of the quarks number. In the region of high transverse momenta this effect must be analyzed in order to have a better comprehension of the different suppression experienced by the hadronic species and have to be compared with the results of the [5,6,7]. We have moreover the intention to include the effect of the mean field in order to give a better description of the QGP. This will be done using a quasi-particle model. We expect that the effect of the masses will increase the ratio between the quark number and the gluon number up to 6 for the region of low p T. This implicate that the bulk should be for mostly composed by quarks. REFERENCES [1] Z. Xu, C. Greiner, Phys. Rev C.71 (2005) ; [2] G. Ferini, M. Colonna, M. Di Toro and V. Greco, Phys. Lett. B 670, 325 (2009); [3] J. F. Owens, E. Reya, and M. Gluck, Phys. Rev. D 18, 1501 (1978); [4] S. Plumari, W M. Alberico, V. Greco, C. Ratti, arxiv : [hep-ph]; [5] F. Scardina, M. Di Toro, V. Greco, Phys. Rev. C 82 (2010) ; [6] W. Liu, C. M. Ko and B. W. Zhang, Phys. Rev. C 75 (2007) ; [7] F. Scardina, M. Di Toro, V. Greco, Nuovo Cim. C34N2 (2011)

105 A STUDY ABOUT DYNAMIC MODELS ON PHOSPHOLIPIDS A. Trimarchi a, * a)dottorato in Fisica dell Università di Messina, Dip.to di Fisica, F.S. D Alcontres,9816 S. Agata-Messina, Italy * Corresponding author, antotrimarchi@unime.it Abstract Model membranes are a first step to understand very complex objects like cell membranes. The former constitute a essential element so that cells work. Membranes are active protagonists in many processes, as material transport and cell signaling. The comprehension of the dynamics in play can give us the possibility to exploit them in several research fields like pharmaceutical industries or medical sciences. In this paper we try to explain some membrane motions by applying several models to the elastic incoherent scattering factor (EISF) like the spherical diffusion or the uniaxial rotation and we show the results. Introduction Membranes are an essential part of the living organisms, playing a fundamental role in several tasks[1]: they surround cells separating them from the external environment. They are composed of amphipathic phospholipids: a hydrophilic head and one or two hydrophobic chains. In a biological membrane there are many different types of lipids as well as many other components besides them, like the proteins, that have important tasks as surface recognition, cytoskeleton contact, signaling, enzymatic activity, or transporting substances across the membrane. Membranes are an important site of cell-cell communication. The complexity of these objects makes their study very difficult so we approximate them with more simple structures, phospholipid bilayers. Phospholipids undergo phase transitions in the temperature range from -10 to 80 C; the main phases belonging to bilayers are the gel phase where the chains are stiff and well ordered, and the liquid phase where the chains are quite disordered. The structures that these phospholipids can form are several ones, depending on lipid concentration, temperature, pressure, and the presence of other substances: they can form bilayer structures, spherical structures, like liposomes, or micelles[2,3]. Dimensionally, important structural quantities to characterize a phospholipid bilayer are the lamellar repeat spacing D, the hydrocarbon chain thickness 2Dc and the average area per lipid A. NMR, X- ray and neutron diffraction[4-6] techniques provided several information about form factors, electron density and scattering length density profiles, while further information and confirmations to experimental models are been obtained by simulations[7]. Nowadays membranes are objects of studying for several research fields and applications[8,9]. In this paper we focus our attention on a QENS study of DMPC(1,2-dimyristoylsn-glycero-3- phosphatidylcholine), and POPC (1-palmitoyl-2-oleoylsn-glycero-3-phosphocholine) phospholipid bilayer, in order to investigate dynamics. Experimental details SAMPLE PREPARATION DMPC and POPC powder sample were purchased from Avanti Polar Lipids. The samples were prepared in order to obtained aligned multilayers following the preparation suggested by Hallock et al.[10]. The lipids were dissolved in a solution 2:1 CHCL 3 /CH 3 OH (chloroform/methanol). After drying the lipid solution, it was joined to a solution 2:1 CHCL 3 /CH 3 OH containing a 1:1 molar ratio of naphthalene (C 10 H 8 ) to lipid so that for each mg of substrate the lipid was dissolved again in 15 μl of this solution. This solution was applied on only one face of the mica sheets, so that we spreaded about 1,5 mg of lipid per cm 2. Naphthalene and any residual organic solvent were removed by means of a vacuum drying overnight. Hydration at 40 C in 96 % relative humidity was indirectly performed using a saturated potassium sulfate D 2 O solution for 12 days, after which 28 moles of D 2 O per mole of lipid are added. Each sample was then built up stacking 6 substrate plates piled with the last foil not spreaded, and was equilibrated at 4 C for 12 additional days. The alignment was then verified by 31 P-NMR chemical shift and with X-ray diffraction. SPECTROMETER The IN5, time of flight (TOF) spectrometer, at ILL Facility (Grenoble), has been used to perform neutron scattering measurements on the phospholipids. This instrument is used to study low-energy transfer processes as a function of momentum transfer, typically, in the region of small energy and momentum transfer values, with an energy resolution of the order of δe/e = 1% (e.g. quasi-elastic scattering in solids, liquids, molecular crystals and inelastic scattering with small energy transfers in the order of magnitude mev). It is characterized by a primary spectrometer in which two synchronized choppers are used to define the incident beam energy, while a third chopper removes unwanted neutrons. A fourth chopper, finally, turning with lower velocity, avoids different pulse overlap. Samples, usually, were run in two orientations for the normal to membrane plane and beam direction. 105

106 At θ = 135, the dynamics are mainly probed in the membrane plane. All scans have been performed starting from an equilibrated liquid crystalline phase hydrated with 28 D 2 O molecules per lipid. the instrumental resolutions. We have assumed as fit parameters the areas of the four functions and the half width at half maximum (HWHM) of the three lorentzian curves: I( ) A ( ) A A A (1) It is interesting to notice that this model fits very well the experimental data as it is clear from the Figure 1 where a semi logarithmic plot is displayed to put the emphasis on residues. From fit parameters of DMPC and POPC it is evident as the A 1, the area of the Gaussian curve (Figure 2), is decreasing with Q. This means that in both case, the dynamics is confined. Furthermore, the HWHMs of the two phospholipids shows us three different dynamics belonging to systems, in so far occur on different timescales and the specific rates of each one differ from other ones at least an order of magnitude (Figure 3). From the areas with several mathematical passages, we can obtain the EISFs of the three motions for the two systems; in particular the fast motion EISF can be obtained easily like 1-A 4. Several models can be used to fit these quantities and obtain information about dynamics concerning the sample and its spatial displacement. Figure 6:Data fits of DMPC sample at 307 K and POPC sample at 298K in 135 orientation. Data have a resolution of 37μeV. Spectra representation is in logarithmic scale to better display lorentzians. DATA ANALYSIS Experimental data have been collected on IN5 at a resolution of 37 μev and with a wavelength λ =8Å. We have measured DMPC+28 D 2 O multi bilayer sample at T = 307 K and POPC+28 D 2 O multi bilayer sample at T = 298 K and both are in liquid phase. Both measurement have been performed in the 135 orientation that gives us information about in-plane motions. Treatment data have been executed with LAMP software, in order to remove bad spectra, correct cross-sections and rebin in energy the time of flight obtained data; afterwards they have been fitted by performing a linear least-square analysis and using Minuit program. The line shape is well represented by the sum of a Delta function and three Lorentzian functions convoluted with Figure 2: POPC areas: the A_1 component (Delta contribution) highlights a confined dynamics. EISFs have been fitted with suitable models by means of Mathematica software. 106

107 the intermediate dynamics is thought like a kink motion, a combination of a rotation plus an out of plane diffusion[14]. Figure 3:HWHM of the three motions. Diffusion (dark points) and rattling motion (blue points). EISF corresponding to the first lorentzian with HWHM = µev can be considered to belong to a diffusion of the atoms around their position[11]. The motion characterized by a HWHM of about 2000 µev is believed to be a fast rotation, called also rattling motion around the molecule axis. The model applied to the corresponding EISF is the uniaxial rotation model[12]: Experimental results From the above relations the shape of the three EISF can be determined (Figure 4). A comparison between POPC and DMPC EISFs (in particular in Figure 5 diffusion EISF) shows as for all three motions the POPC structure factors are always higher than DMPC ones. This means POPC is characterized by a dynamics slower than DMPC one; hypothesis about this experimental fact can be ascribed to acyl chains more long in the POPC, and then a more molecular weight; the presence of a double bond between carbon atoms in one of this POPC chain could likely entail a decreased mobility of the whole system. where EISF m j QR S (2) 2 2 (2 1) m( ) m( ) m 0 S m ( ) 2sinh 0 P (cos ) exp( cos ) d m is an order parameter e P m is the Legendre polynomials of order m. The δ parameter provides information about how the motion of the atom has a distribution in a direction: greater the parameter, more directional the distribution[13]. A limit case is δ = 0 that corresponds to an uniform distribution. The EISF concerning the HWHM of about 100 µev is not quite clear yet, and other studies are requested to give it an accurate meaning. For the experimental setup specifications, free diffusion of lipids is too slow to be observed, and it is hidden inside the experimental resolution. In literature, there are several models to explain these motions. The slow motion is considered like a diffusion in a restricted volume or, or like a ballistic motion with a long range transport on a nanometre scale with a Gaussian-like model[14-16]. The fast motion is considered like a rattling motion [15], while (3) Figure 4: EISF of the motions concerning the hydrogen atoms of the fatty acid chain of POPC. The EISF corresponding to rattling motion is displayed in Figure 6 with the fit curve. The formula (2) was cut off after sixth order to calculus limits of the computer used to run Mathematica. The value of R in the formula was inserted like a constant and equal to the C-H bond length: R = 1.1 Å. The formula was modified with the adding of a normalization parameter, A, to have at Q = 0 Å -1 an unitary value of EISF. The model fits quite well both EISF samples and provides for the parameters the following values; for DMPC sample, δ = 2.45, A = , while for POPC sample, δ = 1.95, A = In the case of DMPC, the experimental points from Q = 1,4 Å -1 to 2.2 Å -1 have been adding from DMPC data obtained in an experiment with wavelength λ = 5 Å. The fit results tell us that the distribution is quite uniform, in particular for the DMPC sample. 107

108 phospholipids in order to observe their influence on this system. Figure 5: EISF comparison between POPC and DMPC samples References [1] R. Lipowsky, E. Sackmann. (1995) Structure and Dynamics of membranes: from cells to vesicles. Handbook of Biological Physics, Vol 1; [2] Jain, M., Introduction to Biological Membranes, 2nd ed., John Wiley & Sons, New York, 1988; [3] Gennis, R.G., Biomembranes. Molecular Structure and Function, Springer-Verlag, New York, 1989; [4] G. Buldt et al., J. Mol. Biol., 134, 673, 1979; [5] G. Zaccai et al., J. Mol. Biol., 134, 693, 1979; [6] J. N. Sachs et al., Biophys. J., 100, 2112, 2011; [7] I. Z. Zubrzycki et al., J. Chem. Phys., 112, 3437, 2000; [8] Immordino ML, Dosio F, Cattel L., Int. J. Nanomedicine 1 (3) (2006) ; [9] Dagenais, C. et al., Eur. J. Phar. Sci., 38(2) (2009) ; [10] K. J. Hallock et al., Biophys. J., 82, 2499, 2002; [11] V. F. Sears, Can. J. Phys. 45, 237 (1967); [12] B. F. Mentzen, Mater. Res. Bull., 1987, 22, 337; [13] M. Bee, Quasielastic Neutron Scattering; Taylor & Francis: 1988; [14] Sackmann, E., Konig, S., Pfeiffer, W., Bayerl, T., Richter, D., J. Phys. II France 2 (1992) ; [15] Busch, S., Smuda, C., Pardo, L. C., Unruh, T., J. Am. Chem. Soc., 2010, 132 (10), pp ; [16] Konig S., Sackmann E., Richter D., Zorn R., Carlile C., Bayerl T. M., J. Chem. Phys. 100 (1994) ; [17] Konig, S., Bayerl, T. M., Coddens, G., Richter, D., Sackmann, E., Biophys. J. 68 (1995), ; [18] Pfeiffer, W., Henkel, T., Sackmann, E., Knoll, W., Richter, D., Europhys. Lett., 8 (2), pp (1989). Figure 6: Fit of the EISF of the rattling motion with the uniaxial rotation model. Conclusion This work has highlighted like our phenomenological model fits very well experimental data bringing out the presence of three distinct motions that involve hydrogen atoms of the phospholipidic hydrophobic chains: an hampered rotation, that we can indicate like a rattling motion, of the hydrogen atom around its position. The other two motions need further studies and the application of other models to be identify with more clarity. The phenomenological model which we have proposed to fit data has provided similar results to other ones available in bibliography[13-18]. The uniaxial rotation model applied to the EISF of the rattling motion gave us information about its distribution width. Successive studies will deal with investigations in normal direction to the membrane (45 orientation) and evaluations of these motions at different temperatures to observe, i. e., how dynamics behaves in the gel phase. A further study will take in consideration the interdigitation of alcohols between 108

109 ULTRAFAST OPTICAL CONTROL OF LIGHT-MATTER INTERACTION AND OF WAVE-PARTICLE DUALITY Rocco Vilardi a, *, Salvatore Savasta a a ) Dipartimento di Fisica della Materia e Ingegneria Elettronica, Università di Messina, I Messina, Italy * Corresponding author, rvilardi@unime.it Abstract A recent article [1] theoretically demonstrated the possibility of an ultrafast control of the wave-particle duality. It exploits a three-level quantum system strongly coupled to a resonant microcavity. The proposed ultrafast optical control can be experimentally realized availing oneself of many different quantum systems ranging from Cooper pair boxes to intersubband polaritons, from semiconductor quantum dots to atomic physics. By sending an opportune sequence of external probe and control pulses it is shown that it is possible to induce a fast coherence sudden death but also it s a coherence sudden birth. Here we theoretically study that process in deeper detail demonstrating that the lost first order coherence is transferred to higher order coherences. Thanks to this process it is, therefore, possible to successively recover first order coherence. We also discuss a new homodyne-like scheme which exploits phase-locked probe pulses in order to experimentally study the wave-particle duality of the considered quantum system and wave particle duality is easily probed just revealing the photons escaping the microcavity. Introduction The principal aim of quantum information science and technology is the control over the modalities of interaction between single photons and individual quantum emitters [2-4]. Thanks to the usage of microcavities, under opportune experimental conditions the strength of the interaction between the quantum emitter and the electromagnetic interaction cavity field can be so intense that light quanta can be absorbed and reemitted many times before escaping the cavity [2,5-9]. In such cases the physical system enters strong coupling regime under which hybrid light-matter quasiparticles arise. Nowadays strong coupling can be achieved and exploited in many experimental physical system ranging from circuit QED [10,11] to atomic systems [12], from quantum dots [13] in optical microcavities to microcavity embedded quantum wells [14]. Moreover, recent studies show the possibility to achieve the so called ultra strong coupling regime. For all these systems, it is important to be able to switch to and from weak coupling regime and to be able to control the time evolution of coherences. A recent article points out the possibility to ultrafast switch on and off the strong coupling regime depending on the order and on the particular times at which pulses are sent [1]. In particular it is demonstrated that not only some internal degrees of freedoms can be in strong coupling while others are in weak coupling regime but the same degree of freedom can show a mix of both weak coupling and strong coupling features. Another important achievement of such an article is the demonstration of an ultrafast technique for erasing the first order photonic coherence explaining such a phenomenology in terms of the fundamental quantum complementarity principle directly connected to the information one can achieve about the quantum physical system. In such an article it is studied the same quantum system discuss in [1]: a single-mode microcavity containing a quantum emitter modeled as a three level fermionic system. The center of the presented research is the study of the modalities of exchange of information between different internal degrees of freedom of the same quantum system and the study of a particular way for controlling and testing the wave-particle duality. In order to conduct our studies we availed ourselves of computational simulations and of a analytical calculations. Theoretical model The point of reference of our theoretical study is the master equation for the density operator where the total Hamiltonian H is being and H i[, H] L (1) H H0 H I H in (2) 0 j j, j aa a j g,1,2 I 1,2.. (3) H g a H c (4) H ( t) a ( t) H. c. (5) * * in p c g,1 109

110 a and, respectively are the destruction operator for the single cavity mode and the transition operator of the levels of a quantum emitter. t represents a Gaussian coherent probe pulses () p resonant both with the g e transition and with the single cavity mode. () t is a control pulse resonant with the s c g transition (see the schemes in figure 1) The realized computational simulations the adopted parameters are: light-matter coupling constant ev, damping g 85 ev, cavity damping 20 of the g level g 2 ev, damping of the e level e 5meV, pure dephasing of the g level d g 0 ev, pure dephasing of the e level d e 0 ev, e 2 g 2.28meV. a emitter is in its fundamental state. A probe pulse is sent to the microcavity. Because it is energetically resonant with the single cavity mode, the cavity photon population abruptly reaches a maximum after which it monotonically decays due to cavity losses. A control pulse is sent in correspondence to the second successive minimum. Because it is energetically resonant with the s g transition, its arrival determines the complete population of the g level. Because of the fact that g e transition is energetically resonant and strongly coupled to the single cavity mode than the cavity photon population aa shows characteristic vacuum Rabi oscillations which are also showed by the squared modulus of its coherent part a 2. By sending another identical control pulse in correspondence to a minimum of aa continues to perform its oscillations while aa, vanishes. As explained in [1] such behaviour is explainable thanks to the fundamental quantum complementarity principle (see figure 2). a 2 Figure 1 left: The quantum emitter is theoretically represented by the following three level scheme. The fundamental quantum state is s. The first and the second excited states respectively are g and e : they respectively are the ground state and the first excited state of the g e transition energetically and strongly coupled to the probe pulse. On the other hand, the s g transition is energetically resonant with the control pulse. Figure 1 right: Microcavity scheme. The quantum emitter (green sphere) is placed within the microcavity which can be externally pumped with probe and control pulses. Transfer of coherence In order to study the temporal evolution of the general quantum state we imposed that the initial quantum state is 0 s : the microcavity is empty while the quantum Figure 2: (Panel a) After the first control pulse both the cavity photon population aa (black dotted line) and the squared modulus of its 2 coherent part a (continuous red line) immediately raise for then monotonically decays due to cavity losses. After the first control pulse strong coupling starts and both begin to oscillate. Cavity photon population continues to oscillate also after a second control pulse sent in correspondence to a minimum. On the other hand, 2 a vanishes. (Panel b) Where 2 2 a vanishes a oscillates. Before the second control sg pulse such coherence was zero but for a short time in correspondence to the arrival of the first control pulse. The zeroing of the 2 a poses a natural question. Where does the information relative to the first order 110

111 photonic coherence go? Is it lost? Is it transferred? And whereto? For trying to investigate such problematic, it is useful to send a third identical control pulse in correspondence to a minimum of aa. The cavity photon population continues to exhibit vacuum Rabi 2 oscillations while the a shows a sudden rebirth and begins to oscillate too. Such phenomenology clearly highlights the fact that the lost-and-then-found first order coherence is transferred to other internal degrees of freedom. The question is now: Where is it transferred? A detailed analysis of higher order coherences allows to find the answer. There exist a coherence which is zero before the arrival of the second control pulse and after the third (it is not zero for a small time in correspondence to the first control pulse) and which oscillates between the second and the third control pulse. Such coherence is 2. The amplitude of its oscillation is exactly that a sg 2 a would have showed if it would have not suddenly died due to the arrival of the second This analysis leads to the conclusion that sg 2 control pulse. 2 a and a exchange their behaviour. In other words, the information relative to internal degrees of freedom (see figure 3). 2 a is transferred to other correspondence to maximum of the cavity photon population, aa begins to monotonically decay and 2 a remains zero. In this case, the coherence is transferred to while, after it, it is transferred to 2 a before the first control pulse sg 2 a which exhibit a monotonic decay. Such a behaviour is really important because it testifies that the transfer of coherence takes into consideration the effects of the modifications induced by external pulses (see figure 4). Figure 4: If the third control pulse is sent in correspondence to the maximum of the cavity photon population then aa monotonically decays, sg 2 a continues to be zero, oscillates between the second and the third control pulse and the 2 sg a monotonically decays sg after the third control pulse. a 2 Homodyne test of wave-particle duality Figure 3: If a third control pulse is sent in correspondence to the minimum of the cavity photon population then aa continues to oscillate while 2 a shows a sudden rebirth and sg 2 a suddenly dies. a is not a physical observable. For this reason, in order to study such property we need indirect measurement. To this end, it is possible to exploit an homodyne technique by which ultrafast testing the waveparticle duality exploring an additional degree of freedom: a relative phase between two phase-locked probe pulses sent after an initial control pulse [14,15]. The transfer of coherence is a general mechanism. Sending, for example, the third control pulse in 111

112 P ( t) Aexp( i t) exp Bexp[ i ]exp a ( t t2) ( t t1) (6) After a control pulse and a successive first probe pulse at , the cavity photon population a t rapidly raises and soon after beginning to oscillate. If a second probe pulse is sent in correspondence to a maximum of aa at t with a relative phase a 0 destructive interference is observed. If, instead, the relative phase is constructive interference is observed. If between the two phase-locked probe pulses it is sent a control pulse then no interference is observable (see figure 5). Figure 6: (Left) The probe pulse is sent at the first cavity photon population maximum and intereference is seen in the degree of freedom. (Right)The same happens if the second probe pulse is sent at the second cavity photon population maximum. but for a phase with respect to that showed in figure 6 left and in agreement with [16]. The three three-dimensional figures thus obtained clearly testify the presence or absence of interference in the degree of freedom. Figure 5:A control pulse is followed by two phaselocked probe pulse. After a second probe pulse sent with a relative phase 0, destructive interference is observed. If the relative phase is then constructive interference is obtained. If between the two phase-locked probe pulse it is sent a control pulse then no interference is observed. In other words, thanks to homodyne-like measurement we can access to information relative to inference also in a physical observable which intensity is. After having observed what happens in three specific cases in which it was imposed that the relative phase is either zero or, we studied the phenomenology with a continuous variation of the relative phase (see figure 6 and 7). Figure 7: No interference is observed if a control pulse is sent betweeen a the two probe pulses. If the second control pulse is sent in correspondence to a cavity population maximum then ce t 0 ( t) c t 1 g d t 0 s (7) g 2 2 The temporal evolution operator U 1 bpa is such that the general quantum state after the first three pulses is ( t) c t 1 g d t 0 s g Noticing that t 2 d t b e 1 s c t 0 e information relative to the phase p b p e (8) i bp e it follows that the degree of freedom is connected only to the coefficient 1 s. If the quantum emitter is in its g state then light is connected to the first 112

113 probe puse. If the quantum emitter is in the e level than the light is connected to the second probe pulse. In other terms, monitoring the state of the quantum emitter we acquire the which-way information about the origin of the photon and, therefore, due to fundamental quantum complementarity principle, interference disappears. On the contrary, if the second control pulse is not sent than it is not possible to get such information and, therefore, interference manifests itsself. Conclusions The presented researches explains the reason why sudden death and sudden ribirth of coherence happen highlighting that the information relative to a coherence can be transferred to other internal degrees of freedoms of the considered physical system. Such achivement is connected to the possibility to experimentally control in an ultrafast way the trasfer of information within a certain physical system thus paving the way to technological quantum information advancements. At the meanwhile, these studies explain the way to ultrafast ontrol wave-particle duality thanks to a homodyne-like detection scheme. The studied scheme could find easy experimental realization thanks to its simplicity. References [1] A. Ridolfo, R. Vilardi, O. Di Stefano, S. Portolan, and S. Savasta, Phys. Rev. Lett. 106, (2011); [2] J. M. Raimond, M. Brune, S. Haroche, Rev. Mod. Phys. 73, 565 (2001); [3] C. Monroe, Nature (London) 416, 238 (2002); [4] L. M. Duan and H. J. Kimble, Phys. Rev. Lett. 92, (2004); [5] C. Weisbuch, M. Nishioka, A. Ishikawa, and Y. Arakawa, Phys. Rev. Lett. 69, 3314 (1992); [6] J. P. Reithmaier, G. Sek, A. Löffler, C. Hofmann, S. Kuhn, S. Reitzenstein, L. V. Keldysh, V. D. Kulakovskii, T. L. Reinecke, and A. Forchel, Nature (London) 432, 197 (2004); [7] T. Yoshie, A. Scherer, J. Hendrickson, G. Khitrova, H. M. Gibbs, G. Rupper, C. Ell, O. B. Shchekin, and D. G. Deppe, Nature (London) 432, 200 (2004); [8] K. Hennessy, A. Badolato, M. Winger, D. Gerace, M. Atatüre, S. Gulde, S. Fält, E. L. Hu, and A. Imamoglu, Nature 445, 896 (2007); [9] I. Chiorescu, P. Bertet, K. Semba, Y. Nakamura, C. J. P. M. Harmans, and J. E. Mooij, Nature (London) 431, 159 (2004); [10] A. A. Abdumalikov, O. Astafiev, A. M. Zagoskin, Yu. A. Pashkin, Y. Nakamura, and J. S. Tsai, Phys. Rev. Lett. 104, (2010); [11] B. Peropadre, P. Forn-Diaz, E. Solano, and J. J. Garcia-Ripoll, Phys. Rev. Lett. 105, (2010); [12] J. McKeever, A. Boca, A. D. Boozer, J. R. Buck, and H. J. Kimble, Nature 425, 268, (2003); [13] A. Dousse, Jan Suffczyński,, A. Beveratos, O. Krebs, A. Lemaître, I. Sagnes, J. Bloch, P. Voisin and P. Senellart, Nature (London) 466, 217, (2010); [14] O. Di Stefano, A. Ridolfo, S. Portolan, and S. Savasta, Opt. Lett. 36 No.22, (2011); [15] R Vilardi, A. Ridolfo, S. Portolan, S. Savasta, O. Di Stefano, Quantum Complementarity of Cavity Photons Coupled to a Three- Level System, to be published by Physical Review A.; [16] O. Di Stefano, R. Stassi, A. Ridolfo, S. Patanè, and S. Savasta, Phys. Rev. B, 84, (2011). 113

114 114

115 SEMINARI (Invited) DEL DOTTORATO DI RICERCA IN FISICA Effettuati nel

116 Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 19 Gennaio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica V.le F. Stagno d Alcontes 31, Messina Prof. Józef SURA Heavy Ion Laboratory (HIL), University of Warsaw, Poland Seminar title: The HIL Cyclotron and associated ion optics Abstract The isochronous cyclotron of the Heavy Ion Laboratory of Warsaw accelerates ions with mass to charge ratio in the range of A/Q=(2-6) and energies up to 30 MeV per nucleon. The design of this setup includes many of the accelerator physics and ion optics elements. These elements beginning with the ECR ion source, injection, acceleration, extraction, beam lines, till the experimental setups will be discussed. Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 7 Febbraio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica V.le F. Stagno d Alcontes 31, Messina Dr. Ernesto Amato Dipartimento di Scienze Radiologiche, Policlinico dell Università di Messina Seminar title: The Geant4 Monte Carlo package from Cern and its applications to nuclear, particle, astroparticle and medical radiation physics Abstract Geant4 (Geometry and Tracking 4) is a Monte Carlo toolkit developed by Cern in object-oriented C++ programming paradigm, for the simulation of nuclear and particle interaction. It offers a wide set of complementary physics models, based either on theory or on experimental data and parametrizations, for electromagnetic and hadronic interactions in energy ranges spanning from some tens of ev to TeV, together with models for nuclear excitation, fission and decay. Extensions to low energy interactions and also to optical photon propagation are available. Complex geometries can be defined and managed, made from elements or compounds whose properties can be obtained from databases or user defined. Volumes can be made sensitive to simulate detectors, through the use of hits and digitisation classes. Primary particles propagate through the defined geometry according to the tracking and stepping rules, obeying to the physics models adopted and to the selected cuts. Interaction tracks and cascades can be visualized either online or offline, and relevant quantities are scored in 1-2-3D histograms and n-tuples. Several ancillary softwares from Cern and from application developer teams aid the user in the I/O phases. After a general introduction to the Geant4 concept, architecture and physical models, I will comment on the different fields of application, spanning from the high energy physics and astrophysics experiments, to the application of radiation physics for dosimetry and radioprotection from sources of photons, leptons and hadrons. 116

117 Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 22 Febbraio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d Alcontres 31, S. Agata, Messina Prof. C.A. Squeri, Prof. V. Candela, Dott. J. Trombetta, Dott. A. M. Roszkowska Ophthalmology Unit, Department of Surgical Specialties, University Hospital of Messina, Messina, Italy. Seminar title: Clinical applications of the different laser platforms in ophthalmology Abstract: The purpose of this seminary is to present the clinical applications of the different lasers in ophthalmology. The following lasers will be presented: Femtosecond lasers. This kind of lasers is characterized by ultrashort pulses. They perform horizontal or vertical corneal cuts and are used in corneal and refractive surgery. They are adopted in corneal lamellar keratoplasty and in refractive surgery. Excimer laser and solid state laser. The characteristics of these lasers are used to modify the anterior corneal shape. Flattening or steppening of the corneal surface permit to correct existing refractive errors, so such lasers are widely used in corneal refractive surgery. Argon laser and diode laser These lasers perform retinal photocoagulation. They create retinal scars with effect on retinal pathologies such as diabetic retinopathy, retinal ruptures or holes and degenerations. NdYAG laser. It is above all a disruptive laser used to treat secondary cataract performing posterior capsulotomy. It is also adopted to resolve an angle closure glaucoma by localized iridotomy (puncture-like openings through the iris without the removal of iris tissue). Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 4 Marzo 2011, ore 10.00, Conference Room CNR-IPCF V.le F. Stagno d Alcontres 37, S. Agata, Messina Seminar title: Ettore Majorana and the Birth of Autoionization Ennio Arimondo Dipartimento di Fisica E. Fermi, Università di Pisa Abstract: In some of the first applications of modern quantum mechanics to the spectroscopy of many-electron atoms, Ettore Majorana in 1931 solved several outstanding problems by developing the theory of autoionization. Later literature makes only sporadic references to this accomplishment. After reviewing his work in its contemporary context, we describe subsequent developments in understanding the spectra treated by Majorana, and extensions of his theory to other areas of physics. We find several puzzles concerning the treatment of Majorana's work in the subsequent literature and the way in which the modern theory of autoionization was developed. The relevant papers are those numbered 3 and 5 in the convenient collection, Ettore Majorana Scientific Papers: On the occasion of the centenary of his birth, ed. G. F. Bassani et al. (SIF, Bologna 2006), where they are accompanied by English translations and commentary. The originals are, respectively, ``I presunti termini anomali dell'elio,"e. Majorana, Il Nuovo Cimento, 8, 78 (1931) and ``Teoria dei tripletti P' incompleti," E. Majorana, Il Nuovo Cimento, 8, 107 (1931). 117

118 Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 24 marzo, alle ore nella sala conferenze del CNR di Messina V.le F. Stagno d Alcontres 37, S. Agata, Messina Seminar Title: Optical Properties of Carbon-based Materials Elefterios Lidorikis Department of Materials Science & Engineering, University of Ioannina, Ioannina GR Greece Abstract: Carbon nanotubes (CNTs), and more recently graphene, have been at the center of nanotechology research, with the search for new technologies based on their mechanical and electrical properties ever increasing. Graphene, a two-dimensional honeycomb lattice of carbon atoms, can be thought of as the building block of other carbon allotropes: it can be wrapped into fullerenes, rolled into CNTs or stacked up into graphite, with many of their properties deriving from graphene. In this presentation we discuss different aspects of the photonic response of graphene and CNTs. After a brief introduction to the basic electronic structure and optical properties of graphene, we discuss recent advances in understanding interference-enhanced (IERS) and surface-enhanced Raman scattering (SERS) phenomena in graphene. Especially in terms of SERS, graphene provides the ideal prototype two-dimensional test-material for its investigation. We discuss recent SERS experiments on graphene and develop a quantitative analytical and numerical theory for its description. Next, we investigate the photonic properties of two-dimensional CNT arrays for photon energies up to 40eV and unveil the physics of two distinct applications: deep-uv photonic crystals and total visible absorbers. We find three main regimes: for small intertube spacing of 20-30nm, we obtain strong Bragg scattering and photonic band gaps in the deep-uv range of 25~35 ev. For intermediate spacing of nm, the photonic bands anti-cross with the graphite plasmon bands resulting into a complex photonic structure, and a generally reduced Bragg scattering. For large spacing >150nm, the Bragg gap moves into the visible and decreases due to absorption. This leads to nanotube arrays behaving as total optical absorbers. These results can guide the design of CNTbased photonic applications in the visible and deep UV ranges. Dottorato di Ricerca in Fisica, Università di Messina Avviso di Seminario 30 Marzo 2010, Ore 15.00, aula E. Majorana, Dipartimento di Fisica, Università di Messina, V.le F. Stagno D Alcontres 31, S. Agata, Messina Prof. Avazbek NASIROV Bogoliubov Laboratory of Theoretical Physics of the Joint Institute for Nuclear Research of Dubna (Russia) Seminar title: "The role of the entrance channel in study of fusion-fission reaction mechanisms " Abstract: Evaporation residues and binary fragments are main products of the heavy ion collisions at beam energies around the Coulomb barrier. The new superheavy elements Z= are the evaporation residues after emission of neutrons from the heated compound nucleus which is formed in the complete fusion of projectile and target nuclei. Due to very small cross section of the synthesis of superheavy elements it is convenient to study the reaction mechanism by the analysis of fusion-fission fragments formed at fission of compound nucleus. But the fusion-fission fragments are mixed with the quasifission and fast fission fragments which are formed without formation of compound nucleus. In this seminar we will discuss the mechanisms and contributions of these three fissionlike processes to help experimentalists at the choice of reactions for the synthesis of new superheavy elements. 118

119 Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 14 Aprile 2011, ore 15.00, Aula E. Majorana, Dipartimento di Fisica V.le F. Stagno d Alcontres 31, S. Agata, Messina Seminar title: Nuclear Energy: how does it work? Dr.ssa Marina Trimarchi Dipartimento di Fisica, Università di Messina Abstract: The possibility to produce energy from nuclear transmutations is a consequence of the Einstein s equation, stating the equivalence between mass and energy. Fission reactions represent a very powerful energy source, showing a yield 2 millions higher than that of fossil fuels, without greenhouse gases emission. Nuclear power plants working principles will be illustrated, with particular attention to safety aspects, in operational mode as well as in case of accident. In particular, differences between various generations reactors will be stressed, starting from old RMBK type (Chernobyl) to the newest EPR type. Other correlated aspects, as nuclear waste disposal and non-proliferation of nuclear weapons will be considered. Finally, due to recent event regarding Fukushima nuclear accident, an overview of the actual nuclear risk and its consequences worldwide will be given. Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 5 Maggio 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d Alcontres 31, S. Agata, Messina Dr.ssa Valentina Venuti Dipartimento di Fisica, Universita di Messina, CNISM, UdR Messina, Viale Ferdinando Stagno D Alcontres 31, P.O. BOX 55, Messina, ITALY. vvenuti@unime.it Seminar title: Vibrational dynamics and chiral recognition in Ibuprofen/ -cyclodextrins inclusion complexes: FTIR-ATR and numerical simulation results Abstract Cyclodextrins are supramolecular host systems able to encapsulate molecules in their hydrophobic cavity via noncovalent interactions. Their chiral recognition properties, not fully characterized yet, are of great relevance in pharmaceutical industry. Here, we studied how the vibrational properties are affected by the chiral recognition process, upon selection of the non-steroidal anti-inflammatory drug Ibuprofen (IBP) in its chiral (R)- and (S)-, and racemic (R, S)- forms, as model guest, and native and modified -cyclodextrins ( -CDs) as model host. The changes induced, as a consequence of complexation, on the vibrational spectrum of IBP, have been studied, in solid phase, by attenuated total reflection Fourier transform infrared FTIR-ATR. The recorded spectra have been compared with the wavenumbers and IR intensities as obtained by simulation for the free and complexed guest molecule. By the temperature-dependent analysis of the vibrational spectra in the C=O stretching region, the complexation mechanism has been discussed. It turned out to be enthalpy-driven, with enantiomers of IBP giving rise to more stable inclusion complexes with respect to the racemate. This combined experimental-numerical approach gave crucial information on the expected different host-guest interactions that drive the chiral recognition process, helpful to put into evidence differences in the conformational properties of the complexes, that are retained a prerequisite for chiral recognition. 119

120 Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 14 Giugno 2011, ore 12.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d Alcontres 31, S. Agata, Messina Dr.ssa Mariapompea Cutroneo Dottorato di Ricerca in Fisica, Università di Messina Seminar title: High Energy proton/ion beams production by sub-ns, kj-laser plasma interaction Abstract The purpose of this seminar is to present some preliminary results recently obtained in the European & International Experiment, directed by Prof. L. Torrisi of Messina University, at the PALS Laboratory of Prague (Czech Republic), under the support given by LASERLAB Europe. Particularly will be presented some preliminary results concerning the plasma generation in forward direction through thin laser irradiated targets, the plasma laser acceleration of protons and ions at energies above 1 MeV, the new detection technique employing Thomson parabola and semiconductor SiC detectors in time-of-flight configuration, and the first measurements of D-D nuclear fusion induced by 4 MeV deutons accelerated by the laser-plasma. The original results and experimental approaches will be discussed in view of a more details descriptions that will be given in the specific scientific Journals. Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 21 Giugno 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d Alcontres 31, S. Agata, Messina Seminar title: Electron correlations in metals: Dynamical mean-field theory Václav Janiš Institute of Physics, Academy of Sciences of the Czech Republic,Prague Abstract Electrons in metals feel only a screened, short-range Coulomb repulsion. In most of the transition metals, lanthanides and actinides electron correlations are not negligible. To describe the correlation effects correctly one needs a reliable description of strong electron correlations. Gross features of weak excitations of the ground state of interacting fermions are described by Fermi-liquid theory. To assess collective phenomena with quantum coherence in heavy metals, it is necessary to go beyond the framework of Fermi liquid. The way to go systematically beyond Fermi-liquid theory is offered by the so-called Dynamical Mean-Field Theory. We review in this talk the underlying ideas of the dynamical mean-field theory originating in the single-impurity Anderson model and the Kondo effect. We further discuss various aspects of presently the most advanced theory of strongly correlated electrons with examples of its application in model and realistic calculations of electronic properties of metals. 120

121 Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 23 Giugno 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d Alcontres 31, S. Agata, Messina Seminar title: Electrical conductivity and charge diffusion in disordered solids Václav Janiš Institute of Physics, Academy of Sciences of the Czech Republic,Prague Abstract: Electrical resistivity (Ohm s law) in solids is caused by the scattering of almost free conduction electrons on impurities and irregularities in the periodic lattice. The basic theoretical tools for description of quantum transport are linear response theory and Kubo formulas. We review in this talk many-body and Green function methods of calculation of the impact of scatterings of electrons on randomly distributed impurities in metals. We stress the necessity of renormalizations of the perturbation expansion in the strength of the impurity potential and of consistency between one- and two-electron Green functions dictated by conservation laws, electron-hole symmetry and and gauge invariance of the electromagnetic system. Finally we discuss disorder-driven metal-insulator transitions due to discharging of the Fermi energy and due to vanishing of diffusion in the limit of strong randomness. Dottorato di Ricerca in Fisica dell Università degli Studi di Messina 28 Giugno 2011, ore 15.00, Aula E. Majorana, Dip.to di Fisica, V.le F. Stagno d Alcontres 31, S. Agata, Messina Seminar title: Il contributo Light-by-Light al momento magnetico anomalo del muone. Stato attuale e prospettive future. D. Moricciani INFN, Sezione di Roma \Tor Vergata", I Roma, Italy 121