HOLMES - The Electron Capture Decay of 163Ho to Measure the Electron Neutrino Mass with sub-ev sensitivity

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Marco Zamboni
8 anni fa
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1 HOLMES - The Electron Capture Decay of 163Ho to Measure the Electron Neutrino Mass with sub-ev sensitivity ERC - Advanced Grant 2013 PI: Prof. S. Ragazzi Host Institution: Istituto Nazionale di Fisica Nucleare (INFN) Additional Beneficiary: Università di Milano-Bicocca (Resp. Sci.: A. Nucciotti) 1

2 The HOLMES experiment is aimed at directly measuring the electron neutrino mass using the electron capture (EC) decay of 163Ho. A measurement fixing the value of the absolute neutrino mass represents a major breakthrough with profound consequences in particle physics and cosmology. In fact, due to their abundance as big-bang relics, massive neutrinos strongly affect the large-scale structure and dynamics of the universe. In addition, the knowledge of the scale of neutrino masses, together with their hierarchy pattern, is invaluable to clarify the origin of fermion masses beyond the Higgs mechanism. The innovation of HOLMES lies in the calorimetric measurement of the energy released in the decay of 163 Ho. This allows to measure all the atomic de-excitation energy, except the fraction carried away by the neutrino. A finite neutrino mass mν causes a deformation of the energy spectrum which is truncated at Q-mν, where Q is the EC transition energy. The sensitivity depends on Q - the lower the Q, the higher the sensitivity - and 163Ho is an ideal isotope with a Q around 2.5keV. The direct measurement exploits only energy and momentum conservation and is therefore completely model-independent. At the same time, the calorimetric measurement eliminates systematic uncertainties arising from the use of external beta sources, as in experiments with beta spectrometers, and minimizes the effect of the atomic deexcitation process uncertainties. HOLMES will deploy a large array of low temperature microcalorimeters with implanted 163Ho nuclei. The resulting mass sensitivity will be as low as 0.4eV. HOLMES will be an important step forward in the direct neutrino mass measurement with a calorimetric approach as an alternative to spectrometry. It will also establish the potential of this approach to extend the sensitivity down to 0.1eV. The cutting edge detection techniques developed for HOLMES will also have an impact in many frontier fields like astrophysics, material analysis, nuclear safety and diagnostic, archaeometry, and quantum communication. 2

3 HOLMES è il coronamento di quasi 20 anni di ricerca nel campo della misura diretta della massa del neutrino dello sviluppo di rivelatori a bassa temperatura HOLMES sfrutta le risorse e le competenze presenti nel Laboratorio Criostati, realizzato presso il Dipartimento di Fisica in collaborazione con l'infn 3

4 Neutrino open questions mass scale: i.e. mass of the lightest ν degenerate (m 1 m 2 m 3 ) or hierarchical masses mass hierarchy: m 1 < m 2 m 3 or m 3 m 1 m 2? ν = ν? i.e. Dirac or Majorana particle? CP violation in the lepton sector normal hierarchy inverted hierarchy mass scale 4

5 Direct neutrino mass measurements kinematics of weak decays with ν emission low Q nuclear beta decays (3H, 187Re...) only energy and momentum conservation no further assumptions 2 approaches with different systematics: spectrometry: spectrometry the β source is outside the detector calorimetry: calorimetry the β source is contained in the detector which measures all the energy released except the ν energy m ν= 0 ΔE=0 m ν> 0 Q-mν Q (Q E)2 m2ν electron kinetic energy 5 mm KATRIN large MAC-E filter spectrometer with 3H MARE/ECHO/HOLMES array of low temperature microcalorimeters with 187Re or 163Ho AgReO4 5

6 thermometer T V particle absorber E T T = E/C electro-thermal link G temperature Calorimetry with low temperature detectors = C/G tim 1 mg of 100 e mk C ~ T 3 (Debye) C ~ J/K ΔErms ~ 1 ev 6 kev x-ray ΔT ~ 10 mk G ~ W/K = C / G ~ 10 ms complete energy thermalization (ionization, excitation heat) calorimetry T = E/C with C total thermal capacity (phonons, electrons, spins...) phonons: C ~ T 3 (Debye law) in dielectrics or superconductors below Tc low T (i.e. T 1K) Erms = (kb T 2 C)1/2 due statistical fluctuations of internal energy E T(t) = E/C e-t/ with = C/G and G thermal conductance 6

7 HOLMES (ERC-Advanced Grant n ) goal neutrino mass measurement: mν statistical sensitivity as low as 0.4 ev prove technique potential and scalability: assess EC Q-value assess systematic errors baseline Transition Edge Sensors (TES) with 163Ho implanted Au absorbers 6.5x1013 nuclei per detector 300 dec/sec ΔE 1eV and τr 1μs 1000 channel array 6.5x Ho nuclei 18μg 3x1013 events in 3 years Project Start: 1 Feb

8 Electron capture end-point experiment Ho + e 163Dy* + e 163 electron capture from shell M1 A. De Rujula and M. Lusignoli, Phys. Lett. B 118 (1982) 429 calorimetric measurement of Dy atomic de-excitations (mostly non-radiative) rate at end-point and ν mass sensitivity depend on Q kev Recommended: Q = kev Measured: QEC = kev. ½ 4570 years few active nuclei are needed O N 2 N 1 QEC = 2.20 kev Q = 2.55 EC kev M 2 m = 0 ev m = 5 ev m = 10 M 1 ev pile-up QEC = kev Nev=1014; fpp=10-6; EFWHM=2eV 8

9 HOLMES tasks Ho isotope production INFN-Ge 163 Ho isotope embedding in detector INFN-Ge 163 single TES optimization and testing INFN-Ge + INFN-MiB/UniMiB TES array design, engineering and testing INFN-Ge + INFN-MiB/UniMiB multiplexed SQUID read-out optimization and testing INFN-MiB/UniMiB room temperature signal processing and in-line analysis INFN-MiB/UniMiB cryogenic set-up INFN-MiB/UniMiB 9

10 Ho production by neutron activation 163 Er (n,γ) 163Er 162 Er 163Ho + νe 163 σthermal 20b τ½ec 75min only few experimental data for almost all cross sections involved possibly high yield Ho nuclei/mg(162er)/h for a thermal neutron flux of 1013 n/cm2/s 163Ho(n,γ)164Ho (burn-up)? 165Ho(n,γ) (from Ho contaminations or 164Er(n,γ)) 166mHo, β τ½=1200y analyse 163Ho content in MARE-RD activated samples ICPMS requires enrichement and oxide chemical form (Er2O3) 10

11 HOLMES detectors Transition Edge Sensors (TES) with Au absorber hot electron microcalorimeters with electro-thermal feedback 2 μm thick electrodeposited Au for full absorbtion MoAu or MoCu proximity TES Tc 100mK on Si2N3 membrane τd 30 μs NASA/GSFC 11

12 HOLMES detector array fabrication single pixel array subcontract array fabrication optimize design for speed and resolution define process for 163Ho implantation subcontractor fabricates array with 1 μm Au absorber Genova completes array fabrication Genova implants Genova covers implant with 1 μm Au absorber Genova completes array fabrication (Si2N3 release) Ho at shallow depth ( 100Å) Ho Ge A. Nucciotti - Giornata FET e ERC presso UNIMIB - 12 marzo

13 HOLMES detector array and multiplexed read-out NIST 13

14 ERC Synergy 2012 (prima call Synergy...) NEXHO PI: S. Ragazzi, F. Gatti, A. Nucciotti HI: INFN STEP 1: valutato B (Ranking range : 25-34%) miglior risultato per i Synergy 2012 proposti dall'infn Ground-breaking Group added value Methodology PIs Quality PIs Commitment referee 1 referee 2 referee 3 referee 4 FG e AN non sono piaciuti Non abbiamo capito cos'è un Synergy... 14

15 ERC Advanced 2013 NEXHO HOLMES PI: S. Ragazzi HI: INFN (Additional beneficiary: Univ. Milano-Bicocca) Milano-Bicocca stesso progetto ma budget ridotto da 9.3M a 3.5M migliorie: CV del PI abstract e synopsis (B1): keywords (ground-breaking, ) inglese (con l'aiuto di un collaboratore americano) STEP 2: valutato A (Ranking range : 1-43%) budget ridotto di altri 0.5M... 15

16 Riflessioni il PI giusto (prestigio personale vs. opportunità di finanziamento)* CV: usare le giuste keywords e la HI? la proposta scritta nel modo giusto capire meccanismi di valutazione dell'erc B1 vs. B2 B1: scritto per non esperti del settore, con tutte le risposte alle possibili critiche imparare il linguaggio della commissione: keywords importanza dell'autovalutazione imparare dai referti (anche di altri progetti...) migliorarsi attraverso sottomissioni ripetute (cambiando PI...) *... These restrictions are designed to allow unsuccessful Principal Investigators the time to develop a stronger proposal.... approfittare dei servizi di supporto e consulenza UniMiB: Area della Ricerca INFN: CSTF - Common Strategic Task Force condizioni al contorno: comunità scientifica amichevole, momento giusto molta fortuna * contrario ai principi dell'erc 16

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