Search for neutrinoless double beta decay: status of SuperNEMO project Yu. Shitov, Imperial

Transcription

1 IPPP-Imperial meeting, Search for neutrinoless double beta decay: status of SuperNEMO project Yu. Shitov, Imperial

2 Double beta decay basic statements (A,Z) (A,Z+1) Q ββ (A,Z+2) ββ2ν: allowed SM process T 1/2 ~ y (A,Z) (A,Z+2) + 2e - + 2ν (2n 2p + 2e - + 2ν) ββ0ν: beyond the SM T 1/ y (A,Z) (A,Z+2) + 2e - (2n 2p + 2e - ) Massive Majorana neutrinos (particle antiparticle) Happiness for theoreticians (many mechanisms proposed to describe the process) (Q ββ ββ ~ MeV) n n W ν er ν el W p h ν M h p e e

3 Double beta decay basic equations 0ν 0ν 1 0ν 0v v 2 = ( 1/2 ) = ( ββ, ) ν / e ~ ββ A T G Q Z M m m Q Z M - effective neutrino Majorana mass M 0ν G 0ν : nuclear matrix element : phase space factor THEORY M ε K C.L. N t N Bckg E : mass (g) : efficiency : confidence level : Avogadro number : exposition time (y) : background events/ (kev/kg/y) : energy resolution (kev) ~ 69 stable and 28 α-unstable ββ isotopes EXPERIMENT

4 Resolution as key point (Q ββ ββ ~ MeV) Avignone, King, Zdesenko, New Journal of Physics 7 (2005) 6

5 Experimental techniques to observe ββ-decay Experimental methods Geochemical & Radiochemical (A,Z-2)daughter ββ-sample (A,Z) Calorimetric Source Detector β β Tracko-calo E 1 E 2 ββ-foil Experimental output θ E 1 TPC E 2 B ββ-foil or ββ-gas ββ-daughter rate E1+E2 spectrum E1, E2, θ

6 Calorimeter versus tracko-calo/tpc detectors Calorimetric Tracko-calo/TPC Experimental advantages Larger mass Better resolution high (~ 100%) efficiency Real ββ-observation. Any ββ-source can be measured Potentially zero-background exp. Test of different ββ0ν mechanisms in the case of observation Experimental drawbacks A few ββ-isotopes can be measured 76 Ge, 130 Te up to now. Unavoidable natural background. We don t see electrons, just energy released - no absolute proof, that we see ββ0ν-peak and not something else (γ-line)! difficult to accept large mass smaller efficiency worth resolution

7 NEMO-3/SuperNEMO collaboration Neutrino Ettore Majorana Observatory (Neutrino Experiment on MOlybdenum historical name) USA MHC INL U Texas Spain U Valencia U Saragossa U Barcelona Morocco Fes U UK Finland Poland Russia U Jyvaskyla U Warsaw UCL U Manchester Imperial College France CEN Bordeaux IReS Strasbourg LAL ORSAY LPC Caen LSCE Gif/Yvette JINR Dubna ITEP Moscow Kurchatov Institute Ukraine INR Kiev ISMA Kharkov Slovakia (U. Bratislava) Czech Republic Charles U Praha IEAP CTU Praha Japan U Saga U Osaka ~ 80 physicists, 12 countries, 27 laboratories. R&D Program for 02/ /2009 is being carring out. Major contributors: UK, France. Smaller but vital contributions from US, Russia, Czech Republic, Japan.

8 20 sectors The NEMO3 detector Fréjus Underground Laboratory : 4800 m.w.e. Source: 10 kg of ββ isotopes cylindrical, S = 20 m 2, 60 mg/cm 2 Tracking detector: drift wire chamber operating in Geiger mode (6180 cells) Gas: He + 4% ethyl alcohol + 1% Ar + 0.1% H 2 O 3 m Calorimeter: 1940 plastic scintillators coupled to low radioactivity PMTs B (25 G) Magnetic field: 25 Gauss Gamma shield: Pure Iron (18 cm) Neutron shield: borated water (~30 cm) + Wood (Top/Bottom/Gapes between water tanks) Able to identify e, e +, γ and α delayed

9 NEMO3 sector PMTs Cathodic rings Wire chamber Calibration tube scintillators ββ isotope foils

10 100 Mo ββ2ν Results 100 Mo 2β2ν results Num mber of events/0.05 MeV Sum energy spectrum NEMO Mo events 6914 g 389 days S/B = 40 Data 2β2ν Monte Carlo Background subtracted Number of events Angular distribution NEMO Mo events 6914 g 389 days S/B = 40 Data 2β2ν Monte Carlo Background subtracted E 1 + E 2 (MeV) T 1/2 (ββ2ν ββ2ν) = 7.11 ± 0.02 (stat) ± 0.54 (syst) years «ββ factory» tool for precision tests 0 Cos(θ)

11 100 Mo 2νββ single energy spectrum as probe of 2νββ mechanism HSD, higher levels contribute to the decay Single electron spectrum different between SSD and HSD Mo Events / 24 kev Tc RAW-BGR spectrum and MTCA 2b2n NEMO-3 HSD higher levels SSD, 1 + level dominates in the decay (Abad et al., 1984, Ann. Fis. A 80, 9) 4.57 kg.y E 1 + E 2 > 2 MeV Data 2β2ν HSD Monte Carlo Background subtracted Simkovic, J. Phys. G, 27, 2233, 2001 E single (kev) RAW-BGR spectrum and MTCA 2b2n χ 2 /ndf = 139. / χ 2 /ndf = 40.7 / 36 Events / 24 kev NEMO-3 SSD Single State 4.57 kg.y E 1 + E 2 > 2 MeV Data 2β2ν SSD Monte Carlo Background subtracted MO100, EE-int, Emin ENRGY E single, kev E single (kev) HSD: T 1/2 = 8.61 ± 0.02 (stat) ± 0.60 (syst) y SSD: T 1/2 = 7.72 ± 0.02 (stat) ± 0.54 (syst) y MO100, EE-int, Emin ENRGY E single, kev E single (kev) 100 Mo 2β2ν single energy distribution in favour of Single State Dominant (SSD) decay

12 Preliminary 0ν2βresults limits ( ) with 100 Mo (7 kg) 693 days of data Phase I + Phase II 693 days of data Phase I + Phase II 100 Mo 82 Se T 1/2 > % C.L. m ν < ( ) ev [1-3] T 1/2 > % C.L. m ν < ( ) ev [1-3] Expected 2009 sensitivity: T 1/2 (ββ0ν ββ0ν) ~ 1-2 x (90 % CL) <m ν > < ev

13 NEMO-3 From NEMO to SuperNEMO SuperNEMO 7 kg 100 Mo T 1/2 (ββ2ν ββ2ν) = y FWHM ~ 12% at 3 MeV (dominated by calorimeter ~ 8%) ε(ββ0ν ββ0ν) = 18 % Mass of isotope Energy resolution (FWHM of the ββ0ν ray) Efficiency kg 82 Se 150 Nd T 1/2 (ββ2ν ββ2ν) = y Total: FWHM 7 % at 1 MeV Calorimeter: 4 % at 3 MeV ε(ββ0ν ββ0ν) ~ 30 % 214 Bi < 300 µbq/kg 208 Tl < 20 µbq/kg ββ2ν ~ 2 cts / 7 kg / y ( 208 Tl, 214 Bi) ~ 0.5 cnts/7 kg/y Internal contaminations in the source foils in 208 Tl and 214 Bi Background (If 82 Se) 214 Bi < 10 µbq/kg 208 Tl < 2 µbq/kg ββ2ν=1, 208 Tl = Bi=0.5 cnts/100 kg/y T 1/2 (ββ0ν ββ0ν) > y <m ν > < ev Sensitivity T 1/2 (ββ0ν ββ0ν) > (1-2) y <m ν > < mev NEMO-3 successful experience shows us that technique can be extrapolated for larger mass next generation detector to reach new sensitivity level. SUPERNEMO R&D is in progress since 2006

14 SuperNEMO basic design Plane geometry Source (40 mg/cm 2 ) 12m 2, tracking volume (~3000 channels) and calorimeter Modular (~5 kg of enriched isotope/module) 100 kg: 20 modules ~ channels for drift chamber ~ / channels for 5 /8 PMT 4 m 1 m 5 m Top view Side view

15 Alternative SuperNEMO sandwich bar design SC bars double sided with PM. Only ~ 3000 relatively cheap (3 5 ) PM (~ PM in basic design). More compact, cheaper, less background from PM, but worse resolution (~10-11%).

16 Calorimeter R&D Baseline design detecting cell with required parameters has been designed

17 Tracker R&D SuperNEMO tracker (major UK responsibility) has been developed including all accessories required (mechanics, electronics, wiring robot, etc.) 90-cell prototype has been built and testing now.

18 R&D for 82 Se sources SuperNEMO collaboration has 6 kg of 82 Se with technology in hand for full chain of source production: enrichment -> purification -> foil preparation Purification Enrichment ECP (Electro-Chemical Plant, Svetlana) Zelenogorsk (Siberia) Chemical purification at INL (US) Source foil preparation Installation of NEMO3 foils (LSM)

19 Low background measurement R&D Prototype of setup for measurement of extra low levels (a few µbq/kg) of radio impurities in SuperNEMO source foils (BiPo) has been developed and successively tested

20 Simulations SuperNEMO SoftWare (SNSW) package has been developed and large scale simulations (GRID-based) is in progress

21 Pre-production prototype (demonstrator module) SuperNEMO UK proposal has been submitted in April The main goals of demonstrator ( ) are: To demonstrate the feasibility of large scale detector component production with required performance parameters (e.g. calorimeter energy and time resolution, tracker efficiency and purity). To measure background contributions from the detector components. To finalize the detector design. To produce a competitive physics measurement with 82 Se covering the region of the Klapdor group claim (1yr of data taking with 6kg of 82 Se in the demonstrator module will have a similar sensitivity to GERDA Phase-I).

22 Baseline design of demonstrator in LSM Selected pure iron bored water tanks 25t 60t 1m 7m 5.9 m 5.4 m 4m 100t 0.5m 32tx2 100t 0.2 m NEMO3 steel plates 0.3 m Wood

23 Alternative bar design of demonstrator in LSM Selected pure iron bored water tanks 7m Radonless air 4m 5.9 m 2.8 m 2.45m 4.4 m 1.5m 0.2 m NEMO3 steel plates 0.3 m Wood

24 0nbb experiments overview World leading double beta-decay projects Experiment Isotope kg T 1/2 yr, 90% CL m ν *, mev Start-up timescale Status HM 76 Ge 15 > finished KDHK claim 76 Ge 15 ( ) (3σ) finished CUORICINO 130 Te 11 > finished NEMO Mo (expect. 2009) running CUORE 130 Te approved GERDA, Phase I 76 Ge approved Phase II 76 Ge ~ approved EXO Xe approved EXO 1t 136 Xe R&D SuperNEMO 82 Se/ 150 Nd 100+ (1-2) R&D COBRA 116 Cd ? R&D * Matrix elements from MEDEX 07 or provided by experiments

25 Roadmap for double beta-decay projects CUORICINO, EXO-200 CUORE,EXO NEMO 3 HM Claim GERDA SuperNEMO , 1t experiments (1 or 2) >2020, >10t experiment

26 Conclusion - The 0νββ νββ decay is a test of physics beyond the Standard Model by the search of the leptonic number violation and would determine the nature of the neutrino (Majorana), absolute neutrino mass scale and neutrino hierarchy. - Several experiments are needed to measure different sources with several techniques. - NEMO-3 technique can be extrapolated at ~100 kg to be sensitive to (1-2) y Only tracko-calo (SuperNEMO) and gas TPC can directly register 0νββ-decay. In the case of discovery only direct methods will allow to determine the process leading to ββ(0ν) : light neutrino exchange, right-handed current, supersymmetry, etc. - 3-year SuperNEMO R&D program is carrying out and it is in good shape. Key challenges are calorimeter resolution, isotope choice, and radio purity. Based on design study results full proposal for 100+ kg detector in Last minute isotope change possible. E.g. CUORE sees the signal in 130 Te. -First module All 20 modules ~2013 -Target SuperNEMO sensitivity: mev by 2016, which is competitive with the other next generation 0νββ-experiments.