Search for Majorana neutrinos and double beta decay experiments - PowerPoint PPT Presentation

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

Majorana Neutrino Neutrino is the only fermion with Q = 0  Neutrino might be a Majorana particle n = n ? Only two n states: CPT | n R , h = +1/2 > | n L , 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

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

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) bb0n  m n  V+A Q bb Energy Sum of the two electrons Process  L = 2 • Majorana neutrino exchange • Right Handed weak current Energy and angular distributions • Majoron production will be different ! • Exchange of SUSY particles

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

Constraints from neutrino oscillations In the case of an standard exchange of a Majorana neutrino Merle & Rodejohann PRD 73, 073012 (2006) Degenerate masses    >   2 50 meV m m m m m n 1 2 3 atm m ν > 50 meV Inverted hierarchy  ν  10 m 50 meV Normal hierarchy ? m ν

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 ~ 3 10 27 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) ~ 3 10 25 N nuclei ( 76 Ge) ≈ 10 × N nuclei ( 100 Mo, 150 Nd) from Duek et al. , Phys. Rev. D 83 (2011)

Sensitivity  N   M avog bb n > 0 ln 2 T T   1 / 2 obs A N bkg excl  M  Large Mass of enriched bb isotopes    High efficiency  N excl  Low background  High energy resolution

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 m Bq/kg For comparison, a standard Al foil: A( 208 Tl) ~ 100 mBq/kg

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

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

Ge diodes

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

76 Ge GERDA (LNGS) (Q bb = 2040 keV)  “Bare” Ge crystals in Liquid Argon - Liq. Argon = cryostat + shield Without PSA With PSA - Ext. Water tank for shield + m -veto - Detector arrays  gradual deployment  Phase 1 (2011-2013) ~ 18 kg 76 Ge 8 old 76 Ge detectors ( HdM, IGEX ) 5 new BEGe detectors FWHM ~ 3 keV @ 2.6 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 ) > 2.1 10 25 yr (90% C.L.) Mod. Phys. Lett. A 29, 1430001 (2014)

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  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 ) > 2 10 26 yr in 5 yrs of data

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

Bolometers

nat Te0 2 crystal CUORICINO (LNGS, Italy) CUORICINO ( 2003 – 2008) ~50 crystals nat TeO 2 40 kg nat Te0 2  ~ 10 kg 130 Te 60 Co FWHM ~ 6 keV @ Q bb T 1/2 ( bb0n ) > 2.8 10 24 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

nat Te0 2 crystal CUORE (LNGS, Italy) CUORE (start 2015) 19 Cuoricino-like towers in a new cryostat 740 kg nat Te0 2  200 kg 130 Te Target: Bkg = 0.01 cts/(keV.kg.yr) Sensitivity expected in 5 years T 1/2 ( bb0n ) > 10 26 y (17 times lower than Cuoricino) 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

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)

Scintillating bolometers Lumineu R&D Ge plate Scintillation signal ZnMoO 4 (313g) a /(e - , g ) discrimination 141 h @ 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 = 10 - 3 – 10 - 4 cts/(keV.kg.y)  T 1/2 ~ 10 26 yrs with only 1 cuoricino-like tower ! (instead of 19…)

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) ~ 2 10 21 yrs  Natural candidate for TPC - Liq. TPC: EXO-200 - 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

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 % FWHM @ Q bb (  E ~ 90 keV) 477.6 days ( Sept. 2011 – Sept. 2013 ), 100 kg.yr T 1/2 ( bb 0 n ) > 1.1 10 25 yrs (90% C.L.) Nature 510, 229 (2014) Bkg = (1.7  0.2 10 - 3 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

NEXT (CANFRANC, SPAIN) Gas Xe TPC ~ 100 – 150 kg Xe gas, >90% enrich. 130 Xe Electroluminescence technique for the TPC readout TDR, JINST 7 (2012) T06001  Better Energy resolution Target:  E = 1 % FWHM @ 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:1211.4838)

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