APPEAL Workshop 19-21 February 2007, Japan Double Beta Present Activities in Europe Xavier Sarazin Laboratoire de l Accélérateur Linéaire Orsay France
Germanium detector Bolometers CdZnTe semiconductors at room T Tracko-Calo: NEMO (see C. Marquet and F. Piquemal s talks)
Heidelberg-Moscow Experiment Data taking 1990 2003 5 cristals diodes enriched 76 Ge ~ 10 kg Exposure time ~ 75 kg.year Part of the collaboration Heidelberg-Moscow claims a ββ0ν discovery @ 4σ (NIM A 522 (2004) 371) ββ0ν ββ0ν All data Zoom at Q ββ = 2039 kev Best value T 1/2 = 1.2 10 25 years <m ν > ~0.1 1 ev Pulse shape Analysis (reject multi-compton events)
The GERDA PROJECT New generation 76 Ge ββ experiment at Gran Sasso. Basic idea: Operation of bare 76 Ge diodes in ultrapure cryogenic liquid (LN 2 or LAr). Background rejection Heidelberg-Moscow bkg ~ 0.1 counts/kev/kg/y Hypothesis: origin of bkg due to external gammas Goal of GERDA: achieve ultimate bkg ~ 0.001 counts/kev/y
The GERDA PROJECT Phase III ~ 100 kg O(100kg) segmented diodes, 10 y of exposure Phase II ~ 35 kg 76 Ge Add new (segmented) 76 Ge diodes Phase I ~ 15 kg 76 Ge Use available 76 Ge diodes from HdM and IGEX T 1/2 (y) 10 27 10 26 10 25 Phase III Phase II (2010) Phase I (2008) 10-2 /(kev kg y) 10-1 /(kev kg y) 10-3 /(kev kg y) 10 24 1 10 10 2 10 3 exposure (kg y)
Present R&D GERDA PHASE I 1st test of a bare prototype detector in LAr in 2006 More than 10 cooling and warming cycles performed. Leakage current increased only at the end. Fixed after reprocessing Stable operation for 2 month.
Present R&D GERDA PHASE I Background suppression by LAr scintillation 20 liters Heidelberg test setup. Reduction factor obtained with the test facility is in agreement with MC Reduction factor is limited by LAr volume rate [hz] -1 10 Ge signal Ge signal with LAr veto bkgd data bkgd data with LAr veto -2 10-3 10-4 10-5 10 0 500 1000 1500 2000 2500 Energy [kev] 232 Th
Present R&D GERDA PHASE I Monte-Carlo of LAr bkg rejection with GERDA design MC Example: Background suppression for contaminations located in detector support Factor 300 reduction 10 7 10 6 208 Tl 10 5 10 4 10 3 10 2 10 1 3 10² 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Present GERDA STATUS GERDA Phase I Mid-2007: Cryostat delivery Summer 2008: comissionning of the 15 kg 76 Ge diode End 2009: confirmation of Klapdor hint?! GERDA Phase II: 37.5 kg of 76 Ge (85% enrichment) produced in Sep. 2005 chemical purity: 99.95 % (not yet sufficient) Stored underground in Belgium until decision on further processing steps First 18-fold segmented Ge diode available and under test for background rejection Majorana project (USA) of segmented Ge diode with standard shield will join GERDA?...
Germanium detector Bolometers CdZnTe semiconductors at room T Tracko-Calo: NEMO (see C. Marquet and F. Piquemal s talks)
CUORICINO Bolometer Te natural: 34% of 130 Te Energy resolution (FWHM) ~ 5-10 kev at 2.5 MeV
CUORICINO DETECTOR Gran Sasso Underground Laboratory (Italy), 3500 m.w.e.
Energy calibration survey
CUORICINO RUNNING Run I: 22 Apr. 2003 27 Oct. 2003 29 crystals 5x5x5 11 crystal 3x3x6 2 crystals 130 Te 3x3x6 Total 130 Te MASS = 59 moles ΔE/E @ 2.6 MeV FWHM = 9.2 kev (bkg spect.) Run II: 7 May 2004 Today 40 crystals 5x5x5 13 crystal 3x3x6 2 crystals 130 Te 3x3x6 Total 130 Te MASS = 83 moles ΔE/E @ 2.6 MeV FWHM = 6.3 kev (bkg spect.) Total exposure (10 may 2006): 8.38 kg.year of 130 Te
CURICINO RESULTS
ANALYSIS OF BACKGROUND in ββ0ν region Coincidence (rejected in ββ0ν analysis) TeO 2 crystal TeO 2 crystal Anti-coincidence (dangerous for ββ0ν search) Cupper In the COINCIDENCE spectrum ONLY CRYSTAL SURFACE contam. contribute In the ANTI-COINCIDENCE bkg spectrum Crystal bulk contaminations determine gaussian peaks at the Q-value of the decay Surface contaminations determine peaks at the α energy, with tails (shape depending on contamination depth)
ANALYSIS OF BACKGROUND in ββ0ν region Background level today in CUORICINO 0.2 counts/kev/kg/y Model of background Important part of background due to 238 U or 232 Th contamination on the surface of crystal and Cu structure facing the detectors surface contamination level: ~ 1 ng/g vs bulk c.l. : < 1 (0.1) pg/g for Cu (TeO 2 ) contamination depth: ~ 5 μm in agreement with direct measurement on Cu
CUORE PROJECT Assembly of 19 tower like CUORICINO 988 cristals Natural Te 741 kg nat TeO 2 = 203 kg 130 TeO 2 Sensivity ββ0ν With 5 years of data taking FWHM = 5 kev @ 2528 kev If Background = 0.01 cps/ (kev.kg.an) T 1/2 (ββ0ν) > 2.1 x 10 26 ans (90% C.L.) If Background = 0.001 cps/ (kev.kg.an) T 1/2 (ββ0ν) > 6.6 x 10 26 ans (90% C.L.) If Background = 0.001 cps/ (kev.kg.an) + enriched cristals T 1/2 (ββ0ν) > 1.9 x 10 27 ans (90% C.L.)
Present R&D Background Rejection for CUORE Current Background in CUORICINO: 0.2 counts/kev.kg.year GOAL for CUORE: 0.01 0.001 counts/kev.kg.year Rejection Factor : 20 200!... α polution on the surface of the bolometers: -> R&D strategy for rejection: Add thin surface bolometers γ ( 208 Tl) polution on the surface of the copper frame: -> R&D strategy: improvement of the cleaning efficiency
Present R&D Background Rejection for CUORE Thin surface Ge bolometer to reject surface contamination Classical pulse Classical pulse BULK EVENT SURFACE EVENT Classical pulse Marisa Pedretti Fast high and saturated pulse
Present R&D Background Rejection for CUORE Very preliminary small prototype 4 SSB detectors in LNGS Hall C Ge slabs not clean, only 75% coverage) In order to test the idea Rejection factor obtained = 2 alfa peaks Germanium 212 Po 216 Po 220 Ra 224 Ra Marisa Pedretti Rise Time [ms]
Germanium detector Bolometers CdZnTe semiconductors at room T Tracko-Calo: NEMO (see C. Marquet and F. Piquemal s talks)
COBRA Use large amount of CdZnTe Semiconductor Detectors At room temperature Array of 1cm 3 CdTe detectors K. Zuber, Phys. Lett. B 519,1 (2001)
Test of the first layer 4x4 diodes Installed at LNGS in April 2006 FWHM = 1.9% @ 2.8 MeV BKG@Q ββ ~10 cts/kev/kg/yr 10 3 is required! Design of the 64 detector array
Expected Sensitivity Experiment Nucleus Mass (kg) NEMO 3 CUORICINO GERDA Phase 1 Phase 2 Phase 3 SuperNEMO CUORE if enrich mt 130 Te 100 Mo 82 Se 130 Te 7 1 10 76 Ge 15 35 300 82 Se 150 Nd nat Te nat Te 130 Te FWHM at Q ββ (kev) 350 350 7 4 4 4 Background Counts/ fwhm.kg.y ~ 0.5 ~ 0.1 ~ 0.2 0.04 0.004 0.004 T 1/2 (0ν) limit (years) 2. 10 24 8. 10 23 4. 10 24 3. 10 25 2. 10 26 6. 10 27 <m ββ > limit (mev) 300-1300 600 1500 250 850 250 780 100 320 20 65 Starting taking data 100 210 0.01 1. 10 26 45 130 2012 6. 10 25 70 2012 700 700 700 5 5 5 0.05 0.005 0.005 2. 10 26 6.6 10 26 2. 10 27 35 120 20 65 2008?? 2012?? Nuclear Matrice elements: Shell Model: Caurier (2004) private com. Stoica et al. (2001) Suhonen et al. (1998 and 2003) QRPA Rodin, Simkovic, Faessler (2005)
Conclusions Strong Double Beta activities in Europe Activities are coordinated through ILIAS European program Several experiments are required to demonstrate a positive signal CUORE, GERDA and SuperNEMO: - Experimental technics are robust and demonstrated - Detectors with ~10 kg have obtained good results (NEMO-3, Heidelberg-Moscow and Cuoricino) - Calorimetric approach has first to demonstrate bkg rejection with 100 kg - Strategy to reject ch a background is well defined - Experiments with 1 ton have no sense today with calorimetric approach due to large bkg. Rejection of the background is the main experimental challenge in double beta research - Rule: if the mass of isotope ββ x 10 -> new source of background to be rejected! - A modular design is necessary for a step-by-step R&D