Masse e Oscillazioni dei Neutrini Lezione IV. Corso di Fisica Nucleare e Subnucleare III

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1 Masse e Oscillazioni dei Neutrini Lezione IV Corso di Fisica Nucleare e Subnucleare III

2 Programma 1. Richiami sull'equazione di Dirac, proiezioni chirali, equazione di Weyl. 2. Chiralità ed elicità. Neutrini di Majorana. Decadimento doppio β. 3. Massa di Dirac e di Majorana. Meccanismo dell'altalena (see-saw). 4. Matrice di mescolamento per tre famiglie. Fasi di Dirac e di Majorana. Oscillazioni nel vuoto per tre famiglie. Violazione di CP. 5.Caso limite di due famiglie. Formule approssimate: one mass dominance. Interpretazione del plot m2 vs sin22θ. Valore sperimentale dei parametri della matrice di mixing. 6. Oscillazioni nella materia, meccanismo MSW. 7. Gli esperimenti. I raggi cosmici. Le oscillazioni dei neutrini atmosferici. Super-Kamiokande. K2K. Le oscillazioni dei neutrini solari: Homestake, SNO. Esperimenti ai reattori. Prospettive future. 2 dicembre

3 Dalla teoria agli esperimenti Nel 1934 la sezione d'urto neutrino-nucleone è calcolata essere dell'ordine di cm2 per neutrini di qualche MeV, cioè 19 ordini di grandezza più piccola della sezione d'urto fotone-protone a energie corrispondenti. [...] there is no practically possible way of observing the neutrino The Neutrino H.A. Bethe, R.E. Peierls, Nature 133 (1934) 532 3

4 Fisica dei neutrini e oscillazioni ν existence postulated ν interaction theory and name Solar ν flux calculation Idea of chlorine detector ν interactions observed Idea of ν oscillation Left-handed ν 2 ν's, νµ,νe Pauli Fermi Bethe Pontecorvo Reines & Cowan Pontecorvo Goldhaber Lederman, Schwartz & Steinberger Solar neutrino deficit ν NC interactions observed and the third ν Solar deficit again, atmospheric(?) ν from SN1987A 3 light neutrino families Solar deficit again Atmospheric ν oscillation Solar ν oscillation confirmed Atmospheric ν oscillation confirmed Davis Gargamelle Perl Kamiokande Kamiokande, IMB LEP Collaborations Gallex, SAGE Super-Kamiokande SNO, KamLand K2K 4

5 Cosmic rays flux CR Induced muon flux Standard rock density: 2.65 g/cm3 At 12,000 MWE (meter water equivalent) deep underground muon from neutrino interactions ~ cosmic ray induced muons 5

6 Atmospheric neutrinos cosmic ray e + e + K e e m R(E) = ( + ) ( e+ e) 2 E < 1GeV e e e e ±20% Eν (GeV) ±5% 6

7 Back of envelope calculation of atmospheric neutrino events in 1 kt detector Flux Cross-section Target mass Z/A Time Φ ~ 2 cm-2 s-1 σ ~ cm2 M ~ nucleons/1kt I ~½ T ~ s/year Ninter =Φ(cm-2 s-1) σ(10-38 cm2) M(nucleons/1kt) I T(s/year) ~ 100 events/kt/year 7

8 νµ/νe Ratio (of Ratios) (1985) Morton salt mines (8000t) (1986) Frejus (900t) (1984) Mont Blanc (150t) (1982) Soudan mines(960t) (1989) Kamioka mines (50,000t) (1996) Prime (contrastanti) indicazioni Kamioka mines (3000t) Confermate da SuperKamiokande (1998) Phys.Rev.Lett.81: ,1998 hep-ex/ Prima indicazione del deficit di νµ dal rapporto νµ/νe (Kamiokande) Indicazioni contrastanti negli anni '80 Osservazione dell'asimmetria up-down (Super-Kamiokande, 1998) 8

9 L/E dei neutrini atmosferici θ DOWNWARD (~15 Km) sin2 2θ= 1 E= 1 GeV m2 = ev2 HORIZON (500 Km) m2 = ev2 m2 = ev2 UPWARD (~13,000 Km) Ampio intervallo di L/E: E~ GeV L~15 13,000 Km 9

10 Super-Kamiokande 1Ring µ-like ~40m ~40m 1Ring e-like 50,000 ton water Cherenkov detector 22.5 kton fiducial volume 1000 m underground (2700 m.w.e.) 11, inch PMTs for inner detector 1,885 8-inch PMTs for outer detector 10

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12 20'' PMT by Hamamatsu Photonics 12

13 Detection of Atmospheric Neutrinos Partially Contained (PC) Contained events Upward through-going muons Upward stopping muons µ One cluster in Outer Detector Interaction in the rock Fully Contained (FC) e or µ No hit in Outer Detector 13

14 Zenith angle dependence < < > > sin22θ > < m2< ev2 at 90% CL > 14

15 More Super-Kamiokande samples of atmospheric neutrinos 15

16 Long Baseline per confermare le oscillazioni dei neutrini atmosferici ad un acceleratore Che distanza? Quale energia? 16

17 K2K Conceptual Layout µ monitor 12GeV protons π+ Al Target + Horn π monitor µ ~1 event/2days ~1011 ν µ /2.2sec ~106 ν µ /2.2sec (/10m 10m) ν µ (/40m 40m) 200m decay pipe SK ν τ ND + 100m ~250km Signature of neutrino oscillation 1. Reduction of νµ events 2. Distortion of νµ energy spectrum 17

18 K2K Layout and Strategy π+ Al Target+Horn νµ µ+ 200m decay pipe 1KT SciFi SciBar MRD π monitor 12GeV protons ~1011 νµ/2.2sec (/10m 10m) ~106 νµ/2.2sec (/40m 40m) µ monitor SK 100m ND ντ ~250km ~1 event/2days Combined (1KT,SciFi,SciBar) fit of Pµ,θµ distributions θ p p µ Near detector flux Far detector flux Beam MC PIMON Hadronic models Hadropr. exp. 18

19 GPS ToF=0.83ms SK ±500µs Decay electron cut. 20MeV Deposited Energy 1.5µs ±5µs TDIFF. (µs) K2K FC 22.5kt 1-Ring 1-R µ-like 1-R e-like Multi Ring No Activity in Outer Detector Event Vertex in Fiducial Volume More than 30MeV Deposited Energy Tspill Eν rec 10-2 No Oscillation 0.003% 4.2σ Best fit value (all region) sin22θ = 1.19 ± 0.23 m2 = (2.55 ± 0.40)x10-3 ev2 (in physical region) sin22θ = 1.0 m2 = (2.76 ± 0.36)x10-3 ev sin22θ (mn-v)eµ-mµ2/2+mnv-v2/2 = (mn-v)-eµ+pµcos θµ DATA MC (7.4%) (6.5%) Absolute Deficit 9 3.1σ m2 (ev2) K2K Result Shape Distortion 2.8σ No oscillation Oscillation Eν rec (GeV) 19

20 Disappearance & Shape NSK (#ν µ ) ENERGY SPECTRUM DISTORTION Eν shape m2[ev2] m2[ev2] ABSOLUTE DEFICIT sin22θ sin22θ Allowed regions from νµ disappearance and distortion of Eν spectrum are consistents 20

21 Minos (Fermilab Soudan) 21

22 Neutrino from the Sun The Standard Solar Model (SSM) predicts the power radiated by the Sun from fusion reactions in its core 98.5% of the Sun power comes from the pp reaction: 4 p 4He+2e++2νe+26.7 MeV L = Js-1 Φ = 2L /Q (1/4πD2) cm-2 s-1 D = m Q = 26.7 MeV = J 22

23 SNU Solar Neutrino Unit Per avere 1 interazione al giorno sono necessari O(1030) nuclei bersaglio, cioè O(106) mol, rivelatori di masse dell'ordine del kt 23

24 Spettro dei neutrini solari Flux (cm 2 s 1 /MeV) Gallium Chlorine Water, D2O Gallium SAGE, Gallex,GNO e + 71 Ga 71 Ge + e- ±1% pp ±10% ±10% 7 7 Be Be ±1.5% pep Water Kamiokande, SuperK x + e- x + e- (ES) ±20% 16% B 8?? hep Bahcall-Pinsonneault 2000 Chlorine Homestake e + 37 Cl 37 Ar + e- E (MeV) D2O SNO x + e- x + e- (ES) e + d p + p + e- (CC) x + d n + p + x (NC) 24

25 Misure del flusso dei neutrini solari SNU SNU -7 Kamiokande (ES) ± Gallex + GNO SAGE Homestake 2.58±0.23 Cl ±0.12 SNO (NC) 0.47±0.02 SuperK (ES) 0.35±0.03 SNO (CC) H2O Ga D2O 1 SNU = captures per target atom B 8 Be 7 pp, pep CNO experiments 25

26 Sudbury Neutrino Observatory (SNO) 1000 tonnes D2O 12 m Diameter Acrylic Vessel 1700 tonnes Inner Buffer H2O 9500 PMTs, 60% coverage 5300 tonnes Outer Shield H2O Urylon Liner and Radon Seal 26

27 Neutrino interactions in SNO ES x + e- x + ein SNO (D2O) as in SK (H2O) Mainly e but also, (1:6) Strong sensitivity CC e + d p + p + e- Good energy measurement e only Weak directionality: 1-1/3cos( ) NC x + d n + p + x Equally sensitive to all Measure the total 8B flux 27

28 SNO: total flux as expected from SSM NC rate as expected from SSM (all neutrinos) CC rate (only νe) is 0.31 SSM ES rate is consistent with Super-Kamiokande and oscillation into νµ,ντ Neutrino differents from νe coming from the Sun! (2002) 28

29 Oscillazioni con anti-neutrini da reattore Probabilità di sparizione 2 2 m L m L + cos θ13 sin 2θ12 sin Pdis sin 2θ13 sin 4 Eν 4 Eν Small oscillation (due to θ 13) ) < 2 km Large oscillation (due to θ 12 ) > 50 km Osc. prob. (integrated over Eν ) vs distance νe disappearance at short baseline(~2 km): unambiguous measurement of θ13 Sin22θ13 = 0.1 m231 = 2.5 x 10-3 ev2 Sin22θ12 = m221 = 8.2 x 10-5 ev2 29

30 Reactor oscillation experiments Several generations of short baseline reactor experiments have set upper limits Chooz (France) set limits on at <E>~6MeV, L~1Km for large and for maximal mixing m2 = 5.5x10-5 ev2 Kamland in Kamioka mine (Japan), first long sin2 2 = baseline reactor experiment Sensitive to many reactors with <L>~175Km Observed/Expected = ± ±

31 Kamland results (2008) Best oscillation fit simultaneously to Kamland and solar neutrino data: 31

32 Oscillation data overview Decades of experimental and theoretical efforts! 32

33 Global fits to oscillation data A coherent and consistent global picture emerged. Global fit of neutrino oscillation experiments gives Still unknown,(hints it might be just below the present limit) mass hierarchy, CP violation phase 33

34 Compiti a casa per i prossimi O(20) anni Quanto vale il terzo angolo di mixing θ13? Ci sono neutrini sterili? I neutrini sono fermioni di Dirac o di Majorana? Nei leptoni c'è violazione di CP? E' la leptogenesi l'origine dell'asimmetria materia/antimateria? Quali sono le proprietà elettromagnetiche dei neutrini? Osserveremo mai i neutrini relic del Big Bang? Saremo sorpresi da risultati inattesi? 34

35 This is the end? There is nothing new to be discovered in physics now. All that remains is more and more precise measurement. Kelvin, c