From Cuoricino to CUORE: approaching the inverted hierarchy region Andrea Giuliani University of Insubria (Como) and INFN Milano-Bicocca On behalf of the CUORE collaboration

Outline of the talk Double Beta Decay: physics and experimental issues 130Te and bolometers Structure of Cuoricino and present results From Cuoricino to CUORE The background: model, investigation and solution Cuoricino and CUORE potential according to recent nuclear calculations Conclusions

Outline of the talk Double Beta Decay: physics and experimental issues 130Te and bolometers Structure of Cuoricino and present results From Cuoricino to CUORE The background: model, investigation and solution Cuoricino and CUORE potential according to recent nuclear calculations Conclusions

Decay modes for Double Beta Decay Double Beta Decay is a very rare, second-order weak nuclear transition which is possible for a few tens of even-even nuclides (A,Z)  (A,Z+2) + 2e- neutrinoless Double Beta Decay (0n-DBD) never observed (except a discussed claim) t > 1025 y  (A,Z)  (A,Z+2) + 2e- + 2ne 2n Double Beta Decay allowed by the Standard Model already observed – t  1019 y  Two decay modes are usually discussed: Process  would imply new physics beyond the Standard Model violation of lepton number conservation mn  0 n  n Observation of 0n-DBD

Electron sum energy spectra in DBD The shape of the two electron sum energy spectrum enables to distinguish among the two different discussed decay modes sum electron energy / Q two neutrino DBD continuum with maximum at ~1/3 Q neutrinoless DBD peak enlarged only by the detector energy resolution

Experimental approaches to direct searches Two approaches for the detection of the two electrons: e- source detector Source  Detector  scintillation gaseous TPC gaseous drift chamber with magnetic field and calorimetry Event reconstruction Low efficiency Low energy resolution e- Source  Detector (calorimetric technique)  scintillation solid-state devices gaseous detectors cryogenic macrocalorimeters (bolometers) No or scarce background identification High efficiency Energy resolution

Outline of the talk Double Beta Decay: physics and experimental issues 130Te and bolometers Structure of Cuoricino and present results From Cuoricino to CUORE The background: model, investigation and solution Cuoricino and CUORE potential according to recent nuclear calculations Conclusions

Properties of 130Te as a DBD emitter 130Te features as a DBD candidate: large phase space, lower background (clean window between full energy and Compton edge of 208Tl photons) excellent feature for reasonable-cost expansion of Double Beta Decay experiments high natural isotopic abundance (I.A. = 33.87 %) high transition energy ( Q = 2530 keV ) encouraging theoretical calculations for 0n-DBD lifetime already observed with geo-chemical techniques ( t 1/2 incl = ( 0.7 - 2.7 )  1021 y) 2n DBD decay observed by a precursor bolometric experiment (MIBETA) and by NEMO3 at the level t 1/2 = ( 5 - 7 )  1020 y Mbb  50 meV  t  2x1026 y

The bolometric technique for 130Te: detector concepts Heat sink T  10 mK Thermal coupling G  4 nW / K = 4 pW / mK Thermometer NTD Ge-thermistor R  100 MW dR/dT  100 kW/mK Energy absorber TeO2 crystal C  2 nJ/K  1 MeV / 0.1 mK Te dominates in mass the compound Excellent mechanical and thermal properties Temperature signal: DT = E/C  0.1 mK for E = 1 MeV Bias: I  0.1 nA  Joule power  1 pW Temperature rise  0.25 mK Voltage signal: DV = I  dR/dT  DT  DV = 1 mV for E = 1 MeV Noise over signal bandwidth (a few Hz): Vrms = 0.2 mV Signal recovery time: t = C/G  0.5 s In real life signal about a factor 2 - 3 smaller Energy resolution (FWHM):  1 keV

A physical realization of bolometers for DBD Energy absorber single TeO2 crystal 790 g 5 x 5 x 5 cm Thermometer (doped Ge chip)

Outline of the talk Double Beta Decay: physics and experimental issues 130Te and bolometers Structure of Cuoricino and present results From Cuoricino to CUORE The background: model, investigation and solution Cuoricino and CUORE potential according to recent nuclear calculations Conclusions

Cuoricino and CUORE Location Cuoricino experiment was installed in Laboratori Nazionali del Gran Sasso L'Aquila – ITALY the mountain provides a 3500 m.w.e. shield against cosmic rays R&D final tests for CUORE (hall C) CUORE (hall A) Cuoricino (hall A)

The CUORICINO set-up CUORICINO = tower of 13 modules, Cold finger Tower Lead shield Same cryostat and similar structure as previous pilot experiment Coldest point The CUORICINO set-up CUORICINO = tower of 13 modules, 11 modules x 4 detector (790 g) each 2 modules x 9 detector (340 g) each M = ~ 41 kg  ~ 5 x 1025 130Te nuclides

Technical results on detector performance Performance of CUORICINO-type detectors (555 cm3 - 790 g): Detector base temperature: ~ 7 mK Detector operation temperature: ~ 9 mK Detector response: ~ 250 mV/ MeV FWHM resolution: ~ 3.9 keV @ 2.6 MeV 238U + 232Th calibration spectrum 60 214Bi Counts (/1.2 keV) 228Ac 40K 208Tl 10 0.6 1.6 2.6 Energy [MeV]

t1/20n (y) > 3.1  1024 y (90% c.l.) CUORICINO results 60Co sum peak 2505 keV ~ 3 FWHM from DBD Q-value MT = 15.53 kg 130Te  y Bkg = 0.18±0.02 c/keV/kg/y 130Te 0nbb t1/20n (y) > 3.1  1024 y (90% c.l.) Mbb < 0.20 – 0.68 eV

CUORICINO was stopped and disassembled  Leave room to a crucial test to compare three different procedures to control Cu surface radiaoctivity

Outline of the talk Double Beta Decay: physics and experimental issues 130Te and bolometers Structure of Cuoricino and present results From Cuoricino to CUORE The background: model, investigation and solution Cuoricino and CUORE potential according to recent nuclear calculations Conclusions

From CUORICINO to CUORE (Cryogenic Underground Observatory for Rare Events) CUORE = closely packed array of 988 detectors 19 towers - 13 modules/tower - 4 detectors/module M = 741 kg  ~ 1027 130Te nuclides Compact structure, ideal for active shielding Each tower is a CUORICINO-like detector Special dilution refrigerator

The CUORE collaboration

CUORE funding and schedule CUORE has a dedicated site in LNGS and the hut construction has started The CUORE refrigerator is fully funded and has already been ordered 1000 crystals are fully funded by INFN and DoE – first batch in Nov 2008 The first CUORE tower (CUORE-0) will be assembled and operated in 2009 CUORE data taking is foreseen in 2012

CUORE sensitivity Mbb < 11 – 60 meV Mbb < 20 – 100 meV Montecarlo simulations of the background show that b ~ 0.001 counts / (keV kg y) is possible with the present bulk contamination of detector materials The problem is the surface background (energy-degraded alpha, beta ) It must be reduced by more than a factor 10 with respect to Cuoricino: work in progress! F0n = 9.2 ´ 1025 ´ ( T [ y ] )1/2 F0n = 2.9 ´ 1026 ´ ( T [ y ] )1/2 5 y sensitivity (1 s) with conservative Assumption: b = 0.01 counts/(keV kg y) FWHM = 10 keV 5 y sensitivity (1 s) with aggressive assumption: b = 0.001 counts/(keV kg y) FWHM = 5 keV Mbb < 20 – 100 meV Mbb < 11 – 60 meV

Outline of the talk Double Beta Decay: physics and experimental issues 130Te and bolometers Structure of Cuoricino and present results From Cuoricino to CUORE The background: model, investigation and solution Cuoricino and CUORE potential according to recent nuclear calculations Conclusions

The CUORE background model Monte Carlo simulation of the CUORE background based on: CUORE baseline structure and geometry Gamma and alpha counting with HPGe and Si-barrier detectors Cuoricino experience  Cuoricino background model Specific measurements with dedicated detectors in test refrigerator in LNGS Results…..

The CUORE background components The only limiting factor Background in DBD region ( 10-3 counts/keV kg y ) Ratio to minimal goal Component 214Bi 60Co sum 208Tl ~ 0.1 c / keV kg y CUORICINO Background Environmental gamma < 1 < 0.1 Apparatus gamma < 1 < 0.1 Crystal bulk The only limiting factor < 0.1 < 0.01 Crystal surfaces < 3 < 0.3 Close-to-det. material bulk < 1 < 0.1 Close-to-det. material surface ~ 20 – 40 ~ 2 – 4 Neutrons ~ 0.01 ~ 0.001 Muons ~ 0.01 ~ 0.001

Strategies for the control of the surface background from inert materials (A) Passive methods  surface cleaning (B) Active methods ( “reserve weapons” and diagnostic) events ID Mechanical action Chemical etching / electrolitical processes / plasma cleaning Passivation Crucial test in progress in the former CUORICINO location  surface sensitive bolometers scintillating bolometers able to separate a from electrons

Outline of the talk Double Beta Decay: physics and experimental issues 130Te and bolometers Structure of Cuoricino and present results From Cuoricino to CUORE The background: model, investigation and solution Cuoricino and CUORE potential according to recent nuclear calculations Conclusions

Can Cuoricino scrutinize the HM claim of evidence? Cuoricino and the HM claim of evidence Evidence of 0nDBD decay claimed by a part of the Heidelberg-Moscow experiment (Klapdor et al.) in the nuclide 76Ge T1/20v (y) = (0.69-4.18)  1025 (3σ range) Klapdor et al. Physics Letters B 586 (2004) 198-212 Best value: 1.19x1025 y mββ= 0.24 – 0.58 eV (3σ range) Nuclear matrix element of Muto-Bender-Klapdor Can Cuoricino scrutinize the HM claim of evidence?

Comparison of experimental results in a given nuclear model (T0n1/2)-1 = G0n |M0n|2 Mbb 2 T1/20v (Klapdor et al.) Choose a nuclear model T1/20v (130Te) 2 / 1 130 76 ) ( v Ge Te M G Klapdor T × = QRPA Tuebingen-Bratislava -Caltech group: erratum of nucl-th/0503063 QRPA Jyväskylä group: nucl-th/0208005 Shell Model: Poves’ talk @ 4th ILIAS Annual Meeting - Chambery For the nuclear models, consider three active schools of thoughts:

Cuoricino and the 76Ge claim of evidence The HM claim half life range (3s) is converted into a corresponding range for 130Te using the three mentioned models 3.1x1024 y Present limit Nuclear models QRPA Tuebingen et al. Shell model QRPA Jyväskylä et al. T1/2 x 1024 y for 130Te

CUORE and the inverted hierarchy region Mbb S. Pascoli, S.T. Petcov Quasi-degenarate Inverted hierarchy ~20 meV ~50 meV Inverted hierarchy band Normal hierarchy Lightest neutrino mass

CUORE and the inverted hierarchy region Mbb band corresponding to the inverted hierarchy band of 130Te half lives Nuclear models T1/2 x 1026 y for 130Te QRPA Tuebingen et al. Shell Model QRPAJyväskylä et al. Nuclear models CUORE_ conservative (5 y) CUORE Aggressive (5 y)

Outline of the talk Double Beta Decay: physics and experimental issues 130Te and bolometers Structure of Cuoricino and present results From Cuoricino to CUORE The background: model, investigation and solution Cuoricino and CUORE potential according to recent nuclear calculations Conclusions

Conclusions Bolometers represent a well established technique, very competitive for neutrinoless DBD search Cuoricino has completed the data taking and has shown to be the most sensitive 0n DBD experiment ever run together with HM; uncertainties in nuclear models prevents from scrutinizing fully the 76Ge evidence claim Cuoricino demonstrates the feasibility of a large scale bolometric detector (CUORE) with high energy resolution and competitive background CUORE, a next generation detector, is funded and will start to take data in 2012 Recent results on background suppression confirm the capability to start to explore the inverted hierarchy mass region

BACK-UP SLIDES

CUORE SCHEDULE

CUORE-0 SCHEDULE

CRYOSTAT SCHEDULE

CALIBRATION 12 sources will be guided inside the cryostat The source: active wire contained in copper crimp tubes, crimped onto a Kevlar string and covered by PTFE heat shrink sleeves 6 will go in between the towers and 6 between the HEX and STILL shield 4 ports on the 300K flange, each of which will host a motion control box with 3 independent sources

MUON VETO