Search for Majorana neutrinos and double beta decay experiments

Transcription

1 Search for Majorana neutrinos and double beta decay experiments Xavier Sarazin Laboratoire de l Accélérateur Linéaire (CNRS-IN2P3, Univ. Paris-Sud 11)

2 Majorana Neutrino Neutrino is the only fermion with Q = 0 Neutrino might be a Majorana particle n = n? Only two n states: CPT n L, h= -1/2 > n R, h= +1/2 > Massive Majorana n Violation of the Leptonic Number Leptogenesis in the Early Universe through the Majorana neutrino See-saw mechanism to explain the small mass of the neutrino Observation of bb0n decay is the most sensitive way to probe Majorana

3 bb2n and bb0n decay For few isotopes, b-decay is forbiden bb2n process (second order b-decay) Q bb Energy Sum of the two electrons

4 bb2n and bb0n decay If neutrino is a Majorana particle bb0n Process For few isotopes, b-decay is forbiden bb2n process (second order b-decay) V+A m n bb0n Energy Sum of the two electrons Q bb Process L = 2 Majorana neutrino exchange Right Handed weak current Majoron production Exchange of SUSY particles Energy and angular distributions will be different!

5 Theoretical predictions In the case of an standard exchange of a Majorana neutrino 0n = T M m 1/ 2 0n 0n ee Phase space factor Nuclear Matrix Element Theoretical uncertainty Effective mass m ee = Constraint by n oscillations i U 2 ei m n i

6 Constraints from neutrino oscillations In the case of an standard exchange of a Majorana neutrino m m Degenerate masses 2 m3 mn > matm m ν > 50meV meV Merle & Rodejohann PRD 73, (2006) Inverted hierarchy 10 mν 50meV Normal hierarchy m ν?

7 Nuclear Matrix Elements Calculated T 1/2 (bb0n) to start exploring the Inverted Hierarchy in the case of exchange of Majorana neutrino m n 50 mev ~ QRPA Tüe. Simkovic, Phys. Rev. C 79 (2009); Fang, Phys. Rev. C 82 (2010) QRPA Jy. Kortelainen, Phys. Rev. C 75 and C 76 (2007) NSM Shell Model Menendez, Nucl. Phys. A818 (2009); Phys. Rev. C 80 (2009) IBM Interacting Boson Model Barea, Phys. Rev. C79 (2009) GCM Generating Coordinate Method Rodriguez, Phys. Rev. Lett. 105 (2010) PHFB Projected Hartree-Fock- Bogoliubov Rath, Phys. Rev. C 82 (2010) ~ N nuclei ( 76 Ge) 10 N nuclei ( 100 Mo, 150 Nd) from Duek et al., Phys. Rev. D 83 (2011)

8 Sensitivity T 1/ 2 bb 0n > ln2 N avog A N M T excl obs bkg M Large Mass of enriched bb isotopes High efficiency N excl Low background High energy resolution

9 Origin of background Cosmic rays and induced g s underground lab High energy g s up to ~ 10 MeV produced by neutron captures Natural radioactivity ( 238 U and 232 Th chain): 208 Tl, 214 Bi, Radon ( 222 Rn) and Thoron ( 220 Rn), a-decay (in case of no e - /a discrimination) 208 Tl: Q b = 2.4 MeV + g 2.6 MeV 214 Bi: Q b = 3.2 MeV Ultra low radioactive detectors: Detector materials: A( 208 Tl) < 1 mbq/kg Source A( 208 Tl) < 1-10 mbq/kg For comparison, a standard Al foil: A( 208 Tl) ~ 100 mbq/kg

10 Current best limits obtained in bb0n search Limits at 90% C.L. T 1/2 (0n) limit (10 24 yrs) yrs m n limit (ev) 1 ev GERDA NEMO-3 Inverted hierarchy Cuoricino Kamland-Zen EXO-200

11 Calorimeters Electron Tracking Ge diodes Ionisation Gerda ( 76 Ge) Majorana ( 76 Ge) Tracko-Calo SuperNEMO ( 76 Se, 150 Nd, 48 Ca) Cuore ( 130 Te) Bolometers Phonon + Scint. Lumineu ( 100 Mo) Lucifer ( 82 Se) Gas Xe TPC Ionisation NEXT ( 136 Xe) Amore ( 100 Mo) Scintillators Scintillations Kamland-Zen ( 136 Xe) SNO+ ( 130 Te) Candles-3 ( 48 Ca) Pixel. CdZnTe Ionisation Cobra ( 116 Cd) Liq. Xe TPC Ionisation+scint. EXO ( 136 Xe)

12 Ge diodes

13 76 Ge GERDA (LNGS) (Q bb = 2040 kev) Bare Ge crystals in Liquid Argon - Liq. Argon = cryostat + shield - Ext. Water tank for shield + m-veto - Detector arrays gradual deployment

14 GERDA (LNGS) 76 Ge (Q bb = 2040 kev) Bare Ge crystals in Liquid Argon - Liq. Argon = cryostat + shield - Ext. Water tank for shield + m-veto - Detector arrays gradual deployment Without PSA With PSA Phase 1 ( ) ~ 18 kg 76 Ge 8 old 76 Ge detectors (HdM, IGEX) 5 new BEGe detectors FWHM ~ MeV for BEGe Energy peaks stable within 1 kev 21.6 kg.yr 76 Ge exposure Bkg ~ 10-2 cts/kev/kg/yr This is 10 times lower than previous Ge experiments! T 1/2 (bb0n) > yr (90% C.L.) Mod. Phys. Lett. A 29, (2014)

15 GERDA (LNGS) 76 Ge (Q bb = 2040 kev) Bare Ge crystals in Liquid Argon - Liq. Argon = cryostat + shield - Ext. Water tank for shield + m-veto - Detector arrays gradual deployment Phase 2 (2014) ~ 50 kg 76 Ge 30 new Broad Energy (BEGe) detectors High pulse shape discrimination performances Single Site (bb0n) / Multi Sites (g bkg) discrimination Detection of Ar scintillation light Liquid Argon as active shield with the scintillation veto Target : Bkg ~ 10-3 cts/kev/kg/yr T 1/2 (bb0n) > yr in 5 yrs of data

16 76 Ge MAJORANA (Q bb = 2040 kev) Under construction in Sanford Underground Laboratory (USA) Up to 40 kg of HBGe crystals Standard shield with electroformed Copper and lead Start data with first cryostat end 2014 LOI between GERDA & MAJORANA Collaborations Intention to merge for O(1 ton) exp. selecting the best technologies

17 Bolometers

18 nat Te0 2 crystal CUORICINO (LNGS, Italy) CUORICINO ( ) 40 kg nat Te0 2 ~ 10 kg 130 Te ~50 crystals nat TeO 2 60 Co FWHM ~ 6 Q bb T 1/2 (bb0n) > y (90%C.L.) Astropart. Phys. 34, 822 (2011) BKG = 0.17 cts/(kev.kg.yr) ~ 70% a s from crystals and Cu surfaces ~ 30% external 2.6 MeV g-ray ( 208 Tl) from cryostat Q bb ( 130 Te) ~ 2530 kev

19 nat Te0 2 crystal CUORE (LNGS, Italy) CUORE (start 2015) 19 Cuoricino-like towers in a new cryostat 740 kg nat Te kg 130 Te Target: Bkg = 0.01 cts/(kev.kg.yr) (17 times lower than Cuoricino) Sensitivity expected in 5 years T 1/2 (bb0n) > y CUORE-0 = 1st CUORE tower running in the cuoricino cryostat Preliminary result of the background measurement a bkg reduced by a factor 6 g bkg still dominated by cuoricino cryostat: we must wait for the new cuore cryostat

20 Scintillating bolometers Expected CUORE bkg = 0.01 cts/(kev.kg.yr) ~ 35 cts/year in the bb0n energy window (fwhm) This is still a high level of bkg! CUORE bkg must be reduced by an extra factor 10 at least! The way to reach a «zero bkg» with bolometers: Rejection 2.6 MeV g-ray bkg use crystal with Q bb > 2.6 MeV ZnMoO4, CaMoO 4 ( 100 Mo, Q bb = 3 MeV) ZnSe ( 82 Se, Q bb = 3 MeV) CdWO4 ( 116 Cd, Q bb = 2.8 MeV) Rejection a bkg Scintillating bolometers for a / (e -,g) discrimination S. Pirro et al. Physics of Atomic Nuclei, 69 (2006)

21 Scintillating bolometers Ge plate Scintillation signal a/(e -,g) discrimination Lumineu R&D ZnMoO 4 (313g) 141 LSM Heat signal Energy measurement 3 experiments are starting: LUMINEU: Zn 100 MoO 4 crystal (France) LUCIFER: Zn 82 Se crystal (Italy) AMORE: 40 Ca 100 MoO 4 crystal (Korea) Expected bkg using CUORICINO contaminations bkg = cts/(kev.kg.y) T 1/2 ~ yrs with only 1 cuoricino-like tower! (instead of 19 )

22 136 Xe TPC Experiments Several advantages to study Xenon Simplest and least costly bb isotope to enrich High bb2n half-life T 1/2 ( 136 Xe) ~ T 1/2 ( 76 Ge) ~ yrs Natural candidate for TPC - Liq. TPC: EXO Gas TPC: NEXT Limitation: 2447 kev g-ray from 214 Bi, very close to Q bb = 2462 kev The energy resolution must be better than ~15 kev (0.6%) at Q bb

23 EXO-200 (WIPP, USA) Liq. Xe TPC (200 kg Xe, 80% enrich. 136 Xe) Fiducial Volume 76.5 kg 136 Xe Anti-correlation ionisation/scintillation E = 3.6 % Q bb ( E ~ 90 kev) days (Sept Sept. 2013), 100 kg.yr T 1/2 (bb0n) > yrs (90% C.L.) Nature 510, 229 (2014) Bkg = ( cts/(kev.kg.yr) 28 cts/(fwhm.yr) Radon ( 214 Bi) dominant bkg 2447 kev g-ray from 214 Bi, very close to Q bb = 2462 kev Next step: Radon suppression Future project: nexo with 5 tons 136 Xe

24 NEXT (CANFRANC, SPAIN) Gas Xe TPC ~ kg Xe gas, >90% enrich. 130 Xe Electroluminescence technique for the TPC readout TDR, JINST 7 (2012) T06001 Better Energy resolution Target: E = 1 % Q bb ( E ~ 25 kev) Results of the NEXT-DEMO (a worst geometry): 1.7% FWHM at 511 kev (extrapolating to 0.77% FWHM at 2.5 MeV) has been obtained Electron tracking by topological detection of the characteristic blob at the end of the track NEXT-DEMO: electrons are identified in 98.5% of the cases JINST 8 P04002 (2013) (arxiv: )

25 Large Liquid Scintillators Reuse the available large liquid scintillator n experiments by loading 136 Xe or nat Te KamLAND KamLAND-Zen with 136 Xe SNO SNO+ with nat Te Advantage: one can measure a large mass of bb isotope Limitation: the background is relatively high and the energy resolution is modest

26 Kamland-Zen 320 kg of 136 Xe loaded in 13 tons Liq. Scint. Xe concentration ~ 2.45 % (~700 kg 136 Xe available in Kamioka mine) Energy resolution fwhm = 10 % (~240 kev) at Q bb Fiducial volume ~ 43 % KamLAND-Zen Phase I 110 Ag contamination from Fukushima fallouts

27 Kamland-Zen KamLAND-Zen Phase II: days (Dec May 2014) 383 kg 136 Xe LS purification Xe purification Film surface cleaning by LS flow 110 Ag reduction factor > 10 bkg ~ 10 cts / (fwhm.yr) R<1m Phase I: T 1/2 (0n) > y Phase II: T 1/2 (0n) > y Phases I+II: T 1/2 (0n) > y (90% C.L.) Next steps KamLAND-Zen Next Phase (funded): New inner balloon with 800 kg of load 130 Xe T 1/2 (bb0n) > yrs KamLAND2-Zen High energy resolution with pressurized Xenon

28 SNO+ SNO detector filled with liquid scint. and load 130 Te 130 Te large nat. abundance (34%) : 0.3% nat Te in 1 kt LS ~ 800 kg 130 Te Fiducial volume ~20% 160 kg 130 Te High light yield of loaded Te liquid scintillator: Energy resolution E ~ 8 % at Q bb High T 1/2 (bb2n) : bb2n bkg reduced LS must be ultra radiopure in 238 U and 232 Th (~BOREXINO) Solar 8 B n is the ultimate bkg! 2 years of data First data foreseen end of 2014 T(bb0n) = y

29 NEMO Tracko-Calo

30 NEMO, a tracko-calo approach NEMO combines a tracking detector and a calorimeter Direct reconstruction of the two electrons Can distinguish a possible bb0n signal to a unknown g line Direct measurement of the various components of background Bkg measured separately with dedicated event topology (e-, e+, g, a)

31 NEMO-3 (LSM Modane) Running from Feb until Jan in Modane Underground Laboratory (4800 m.w.e.) Source: ~ 20 m 2 of bb sources foils (~50 mg/cm 2 ) bb0n: 7 kg of 100 Mo, 1 kg of 82 Se bb2n: 0.4 kg 116 Cd, 37 g 150 Nd, 9 g 96 Zr, 7 g 48 Ca Tracking detector: drift cells in Geiger mode Calorimeter: ~ 2000 plastic scint. + 5 PMTs E/E ~ 15% 1 MeV Display of a bb0n candidate

32 NEMO-3 (LSM Modane) 34.3 kg.yr 100 Mo, T 1/2 (0n) > yrs (90% C.L.) bb events E TOT (MeV) NEMO-3 bkg 0.4 cts/(kg.yr) cos

33 SuperNEMO (LSM Modane) NEMO-3 extrapolation 100 kg of 82 Se to reach T 1/2 (bb0n) years Bkg must be reduced by a factor ~ 40 Source: ~ 5 3 m 2 foil (40 mg/cm 2 ): 82 Se, 150 Nd, 48 Ca Tracking: Drift cells in Geiger mode Calorimeter: plastic scintillators + 8" PMT s 20 modules to be installed in the future extension of LSM First module (demonstrator) in construction Start data end 2015 in Modane Target: bkg < 10-2 cts/(kg.yr) in the bb0n ROI NEMO-3 bkg = 0.4 cts/(kg.yr)

34 CONCLUSIONS : New generation of bb experiments with few 100 kg of isotope Experiments using 136 Xe provided already first results with ~100 kg! Kamland-Zen (using available large liquid scint. detector) EXO-200 Liq. TPC New experiments started GERDA Phase 1: results in Summer 2013 Target bkg Phase-1 has been reached : bkg ~ 0.01 cts/(kev.kg.y) GERDA Phase 2 is starting: Target bkg ~ cts/(kev.kg.yr) with 50 kg 82 Ge CUORE-0 : preliminary results bkg is at least 2 times too high New experiments in construction LUCIFER & LUMINEU: scintillating bolometer to reach bkg 0.001cts/(keV.kg.yr) Can measure Se and Mo SNO+ with natural Te: can start measuring ~ 160 kg of 130 Te in 2015 And even larger mass (up to 8 tons?) if the bkg is low enough SuperNEMO with the direct detection of the two emitted e - NEXT-100 (gaseous Xe TPC)

35 SUMMARY Experiment Isotope Mass (kg) 0n bb (fwhm) (kev) bb cts/(fwhm.y) T 1/2 (0n) limit (10 26 yrs) m n limit (ev) Start Data GERDA-I GERDA-II GERDA-III 76 Ge Published 2014? Majorana 76 Ge CUORE 130 Te ZnSe (1 tower) ZnMoO 4 (1 tower) ZnMoO 4 (19 towers) Kamland-Zen Next-Phase SNO+ EXO-200 Rn removed 82 Se 100 Mo 100 Mo 136 Xe 130 Te 130 Xe (0.3%) 8000 (3%) Few tens 28? R&D Published Published 2015 NEXT Xe SuperNEMO 82 Se 82 Se 150 Nd ?? N.M.E. from Duek et al., Phys. Rev. D 83 (2011) In italic: performances already achieved Otherwise, numbers must be demonstrated

36 EXTRA SLIDES

37 Current best limits obtained in bb0n search Isotope Experiment Technique Mass of isotope bb0n Bkg cts /(kg.y.fwhm) T 1/2 (0n) Limit (90%) m n (ev) Min. Max. 48 Ca CANDLES Scintillation 0.01 kg ~ 1 - > Ge GERDA Ionisation 20 kg ~ > Se NEMO-3 Tracko-calo 1 kg ~ > Mo NEMO-3 Tracko-calo 7 kg ~ > Cd Solotvina Scintillation 80 g ~ 1 - > Te CUORICINO Bolometer 10 kg ~ > Xe EXO-200 TPC Xe liq 160 kg ~ > Xe Kamland-Zen Liq. Scint. 130 kg ~ m Ag > Nd NEMO-3 Tracko-calo 0.04 kg ~ >

38 Natural radioactive chains

39 Low Q bb Low 0n 34% nat. abundance Large available mass Low Qbb Bi g ray at

40 Experiment GERDA-I GERDA-II GERDA-III Isotop e 76 Ge Mass (kg) n E@Q bb (fwhm) (kev) bkg@q bb cts/(fwhm. y) T 1/2 (0n) limit (10 26 yrs) m n limit (ev) Start Data Publishe d 2014? Majorana 76 Ge CUORE 130 Te ZnSe (1 tower) ZnMoO 4 (1 tower) ZnMoO 4 (19 towers) Kamland-Zen Next-Phase SNO+ EXO-200 Rn removed 82 Se 100 Mo 100 Mo 136 Xe 130 Te (0.3%) 8000 (3%) Xe Few tens 28? R&D Publishe d Publishe d 2015 NEXT Xe N.M.E. from Duek et al., Phys. Rev. D 83 (2011) In italic: performances already achieved Otherwise, numbers must be demonstrated 82 SUMMARY