Double Beta Present Activities in Europe

Size: px

Start display at page:

Download "Double Beta Present Activities in Europe"

Eugene Hodge
5 years ago
Views:

1 APPEAL Workshop February 2007, Japan Double Beta Present Activities in Europe Xavier Sarazin Laboratoire de l Accélérateur Linéaire Orsay France

2 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.

3 Heidelberg-Moscow Experiment Data taking cristals diodes enriched 76 Ge ~ 10 kg Exposure time ~ 75 kg.year Part of the collaboration Heidelberg-Moscow claims a ββ0ν 4σ (NIM A 522 (2004) 371) ββ0ν ββ0ν All data Zoom at Q ββ = 2039 kev Best value T 1/2 = 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).

4 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 ~ counts/kev/y

5 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) Phase III Phase II (2010) Phase I (2008) 10-2 /(kev kg y) 10-1 /(kev kg y) 10-3 /(kev kg y) exposure (kg y)

6 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.

7 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] Ge signal Ge signal with LAr veto bkgd data bkgd data with LAr veto Energy [kev] 232 Th

8 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 Tl ²

9 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 chemical purity: % (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?...

10 Germanium detector Bolometers CdZnTe semiconductors at room T Tracko-Calo: NEMO (see C. Marquet and F. Piquemal s talks)

11 CUORICINO Bolometer Te natural: 34% of 130 Te Energy resolution (FWHM) ~ 5-10 kev at 2.5 MeV

12 CUORICINO DETECTOR Gran Sasso Underground Laboratory (Italy), 3500 m.w.e.

14 Energy calibration survey

15 CUORICINO RUNNING Run I: 22 Apr Oct crystals 5x5x5 11 crystal 3x3x6 2 crystals 130 Te 3x3x6 Total 130 Te MASS = 59 moles 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 2.6 MeV FWHM = 6.3 kev (bkg spect.) Total exposure (10 may 2006): 8.38 kg.year of 130 Te

16 CURICINO RESULTS

17 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)

18 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

data taking FWHM = 5 kev @ 2528 kev If Background = 0.01 cps/ (kev.kg.an) T 1/2 (ββ0ν) > 2.

19 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 = kev If Background = 0.01 cps/ (kev.kg.an) T 1/2 (ββ0ν) > 2.1 x ans (90% C.L.) If Background = cps/ (kev.kg.an) T 1/2 (ββ0ν) > 6.6 x ans (90% C.L.) If Background = cps/ (kev.kg.an) + enriched cristals T 1/2 (ββ0ν) > 1.9 x ans (90% C.L.)

20 Present R&D Background Rejection for CUORE Current Background in CUORICINO: 0.2 counts/kev.kg.year GOAL for CUORE: counts/kev.kg.year Rejection Factor : !... 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

21 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

22 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]

23 Germanium detector Bolometers CdZnTe semiconductors at room T Tracko-Calo: NEMO (see C. Marquet and F. Piquemal s talks)

24 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)

25 Test of the first layer 4x4 diodes Installed at LNGS in April 2006 FWHM = 2.8 MeV BKG@Q ββ ~10 cts/kev/kg/yr 10 3 is required! Design of the 64 detector array

26 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 Ge Se 150 Nd nat Te nat Te 130 Te FWHM at Q ββ (kev) Background Counts/ fwhm.kg.y ~ 0.5 ~ 0.1 ~ T 1/2 (0ν) limit (years) <m ββ > limit (mev) Starting taking data ?? 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)

27 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

THE CRYOGENIC UNDERGROUND OBSERVATORY FOR RARE EVENTS: STATUS AND PROSPECTS

THE CRYOGENIC UNDERGROUND OBSERVATORY FOR RARE EVENTS: STATUS AND PROSPECTS Eric B. Norman Dept. of Nuclear Engineering Univ. of California, Berkeley, CA U. S. A. Recent results in n physics Neutrinos