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

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

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

Decay modes for Double Beta Decay (A,Z)  (A,Z+2) + 2e - neutrinoless Double Beta Decay (0 -DBD) never observed (except a discussed claim)  > y  (A,Z)  (A,Z+2) + 2e e 2 Double Beta Decay allowed by the Standard Model already observed –   y  Two decay modes are usually discussed: Double Beta Decay is a very rare, second-order weak nuclear transition which is possible for a few tens of even-even nuclides Process  would imply new physics beyond the Standard Model violation of lepton number conservation m  0  Observation of 0 -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-e- e-e- Source  Detector (calorimetric technique)   scintillation  solid-state devices  gaseous detectors  cryogenic macrocalorimeters (bolometers) No or scarce background identification High efficiency Energy resolution e-e- e-e- source detector Source  Detector   scintillation  gaseous TPC  gaseous drift chamber with magnetic field and calorimetry Event reconstruction Low efficiency Low energy resolution

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

Properties of 130 Te as a DBD emitter  high natural isotopic abundance (I.A. = %)  high transition energy ( Q = 2530 keV )  encouraging theoretical calculations for 0  DBD lifetime  already observed with geo-chemical techniques (    incl = ( )  y)  2 DBD decay observed by a precursor bolometric experiment (MIBETA) and by NEMO3 at the level    = ( )  y excellent feature for reasonable-cost expansion of Double Beta Decay experiments large phase space, lower background (clean window between full energy and Compton edge of 208 Tl photons)  M    50 meV   2x10 26 y 130 Te features as a DBD candidate:

The bolometric technique for 130 Te: detector concepts  Temperature signal:  T = 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:  V = I  dR/dT   T   V = 1 mV for E = 1 MeV  Noise over signal bandwidth (a few Hz): V rms = 0.2  V  Signal recovery time:  = C/G  0.5 s In real life signal about a factor smaller Energy resolution (FWHM):  1 keV Heat sink T  10 mK Thermal coupling G  4 nW / K = 4 pW / mK Thermometer NTD Ge-thermistor R  100 M  dR/dT  100 k  Energy absorber TeO 2 crystal C  2 nJ/K  1 MeV / 0.1 mK Te dominates in mass the compound Excellent mechanical and thermal properties

A physical realization of bolometers for DBD Energy absorber single TeO 2 crystal  790 g  5 x 5 x 5 cm Thermometer (doped Ge chip)

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

Cuoricino and CUORE Location Cuoricino experiment is 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)

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 Te nuclides The CUORICINO set-up Cold finger Tower Lead shield Same cryostat and similar structure as previous pilot experiment Coldest point

Technical results on detector performances Energy [MeV] Counts (/1.2 keV) U Th calibration spectrum 208 Tl 214 Bi 40 K 228 Ac Performance of CUORICINO-type detectors (5  5  5 cm g):  Detector base temperature: ~ 7 mK  Detector operation temperature: ~ 9 mK  Detector response: ~ 250  V/ MeV  FWHM resolution: ~ MeV

130 Te 0  60 Co sum peak 2505 keV ~ 3 FWHM from DBD Q-value   /2 0 (y) > 3.0  y (90% c.l.)  M   < 0.20 – 0.98 eV CUORICINO physics results MT = kg 130 Te  y Bkg = 0.18±0.02 c/keV/kg/y Compilation of NME contained in Rodin et al. Nucl. Phys. A 2006 Average FWHM resolution for 790 g detectors: 7 keV

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

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

The CUORE collaboration ITALY UNITED STATES

CUORE funding and schedule  CUORE has a dedicated site in LNGS and the construction will start soon  The CUORE refrigerator is fully funded and has already been ordered  1000 crystals are fully funded by INFN and DoE  The first CUORE tower will be assembled in 2008 and operated in 2009 CUORE data taking is foreseen in 2011

CUORE sensitivity Montecarlo simulations of the background show that b ~ 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! F 0  = 9.2   ( T [ y ] ) 1/2 F 0  = 2.9   ( T [ y ] ) 1/2 5 y sensitivity (1  ) with conservative Assumption: b = 0.01 counts/(keV kg y) FWHM = 10 keV 5 y sensitivity (1  ) with aggressive assumption: b = counts/(keV kg y) FWHM = 5 keV  M   < 20 – 100 meV  M   < 11 – 60 meV

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

The CUORE background model The sources of the background 1.Radioactive contamination in the detector materials (bulk and surface) 2.Radioactive contamination in the set-up, shielding included 3.Neutrons from rock radioactivity 4.Muon-induced neutrons Monte Carlo simulation of the CUORE background based on: 1.CUORE baseline structure and geometry 2.Gamma and alpha counting with HPGe and Si-barrier detectors 3.Cuoricino experience  Cuoricino background model 4.Specific measurements with dedicated detectors in test refrigerator in LNGS Results…..

The CUORE background components Component Background in DBD region ( counts/keV kg y ) Environmental gamma Apparatus gamma Crystal bulk Crystal surfaces Close-to-det. material bulk Close-to-det. material surface Neutrons Muons < 1 < 0.1 < 3 < 1 ~ 20 – 40 ~ 0.01 The only limiting factor

The Cuoricino background and the surface radioactivity model 214 Bi 60 Co p.u. 208 Tl ~ 0.11 c / keV kg y Gamma region

Reconstruction of the Cuoricino spectrum in the region 2.5 – 6.5 MeV 0 DBD Additional component required here

The additional component: inert material surface contamination In order to explain the MeV region BKG, one has to introduce 238 U or 210 Pb surface contamination of the copper structure facing the detectors

(A) Passive methods  surface cleaning (B) Active methods ( “reserve weapons” and diagnostic )  events ID  Mechanical action  Chemical etching / electrolitical processes  Passivation Strategies for the control of the surface background from inert materials  surface sensitive bolometers ‚scintillating bolometers able to separate  from electrons Claudia Nones’ talk in DM parallel section

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

Can Cuoricino scrutinize the HM claim of evidence? T 1/2 0v (y) = ( )  (3σ range) m ββ = 0.24 – 0.58 eV (3σ range) Klapdor et al. Physics Letters B 586 (2004) Best value: 1.19x10 25 y Nuclear matrix element of Muto-Bender-Klapdor Cuoricino and the HM claim of evidence Evidence of 0 DBD decay claimed by a part of the Heidelberg-Moscow experiment (Klapdor et al.) in the nuclide 76 Ge

T 1/2 0v (Klapdor et al.) T 1/2 0v ( 130 Te)Choose a nuclear model Comparison of experimental results in a given nuclear model / / )( )( v Ge v Te v Ge v Te v v M M G G KlapdorT TeT   (T 0 1/2 ) -1 = G 0 |M 0 | 2  M   2  QRPA Tuebingen-Bratislava -Caltech group: erratum of nucl-th/  QRPA Jyväskylä group: nucl-th/  Shell Model: Poves’ 4th ILIAS Annual Meeting - Chambery For the nuclear models, consider three active schools of thoughts: C. Nones, talk at. DBD06 Workshop, ILIAS-WG1, Valencia, April 2006

T 1/2 x y for 130 Te QRPA Jyväskylä et al. Shell model QRPA Tuebingen et al. Cuoricino and the 76 Ge claim of evidence 7x10 24 y Final sensitivity 3x10 24 y Present limit The HM claim half life range (3  ) is converted into a corresponding range for 130 Te using the three mentioned models Nuclear models

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

CUORE and the inverted hierarchy region  M   band corresponding to the inverted hierarchy band of 130 Te half lives Nuclear models T 1/2 x y for 130 Te QRPA Tuebingen et al. Shell Model QRPAJyväskylä et al. Nuclear models CUORE_ conservative (5 y) CUORE Aggressive (5 y)

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

Conclusions  Bolometers represent a well established technique, very competitive for neutrinoless DBD search  Cuoricino is presently the most sensitive 0  DBD running experiment, with a high chance to confirm the HM claim of evidence if this is correct  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 2011  Recent results on background suppression confirm the capability to start to explore the inverted hierarchy mass region