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From Cuoricino to CUORE: towards the inverted hierarchy region

From Cuoricino to CUORE: towards 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. 130 Te and bolometers.

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From Cuoricino to CUORE: towards the inverted hierarchy region

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

  2. 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

  3. 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

  4. 2n Double Beta Decay allowed by the Standard Model already observed – t 1019 y  Two decay modes are usually discussed: neutrinoless Double Beta Decay (0n-DBD) never observed (except a discussed claim) t > 1025 y  (A,Z)  (A,Z+2) + 2e- (A,Z)  (A,Z+2) + 2e- + 2ne Process would imply new physics beyond the Standard Model violation of lepton number conservation mn 0 n  n Observation of 0n-DBD 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

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

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

  7. 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

  8. Properties of 130Te as a DBD emitter 130Tefeatures 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 1/2incl = ( 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

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

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

  11. 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

  12. R&D final tests for CUORE (hall C) 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 CUORE (hall A) Cuoricino (hall A)

  13. Coldest point Cold finger Tower Lead shield Same cryostat and similar structure as previous pilot experiment 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 1025130Te nuclides

  14. Technical results on detector performances • 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]

  15. CUORICINO physics results 60Co sum peak 2505 keV ~ 3 FWHM from DBD Q-value MT = 11.83 kg 130Te  y Bkg = 0.18±0.02 c/keV/kg/y Average FWHM resolution for 790 g detectors: 7 keV 130Te 0nbb Compilation of NME contained in Rodin et al. Nucl. Phys. A 2006 t1/20n(y) > 3.0  1024 y (90% c.l.) Mbb< 0.20 – 0.98 eV

  16. 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

  17. CUORE = closely packed array of 988 detectors 19 towers - 13 modules/tower - 4 detectors/module M = 741 kg  ~ 1027130Te nuclides Compact structure, ideal for active shielding Each tower is a CUORICINO-like detector Special dilution refrigerator From CUORICINO to CUORE(Cryogenic Underground Observatory for Rare Events)

  18. ITALY UNITED STATES The CUORE collaboration

  19. 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

  20. 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! 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 F0n = 9.2 ´ 1025´ ( T [ y ] )1/2 F0n = 2.9 ´ 1026´ ( T [ y ] )1/2 Mbb< 11 – 60 meV Mbb< 20 – 100 meV CUORE sensitivity

  21. 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

  22. 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 model The sources of the background • Radioactive contamination in the detector materials (bulk and surface) • Radioactive contamination in the set-up, shielding included • Neutrons from rock radioactivity • Muon-induced neutrons

  23. The CUORE background components Background in DBD region ( 10-3 counts/keV kg y ) Component Environmental gamma < 1 Apparatus gamma < 1 The only limiting factor Crystal bulk < 0.1 Crystal surfaces < 3 Close-to-det. material bulk < 1 Close-to-det. material surface ~ 20 – 40 Neutrons ~ 0.01 Muons ~ 0.01

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

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

  26. The additional component: inert material surface contamination In order to explain the 2.0 - 4 MeV region BKG, one has to introduce 238U or 210Pb surface contamination of the copper structure facing the detectors

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

  28. 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

  29. 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 Nuclear matrix element of Muto-Bender-Klapdor mββ= 0.24 – 0.58 eV (3σ range)

  30. 0 v T ( Klapdor ) = 0 130 v 1 / 2 T ( Te ) 1 / 2 2 0 v M 0 v G 130 Te 130 × Te 0 0 v v G M 76 76 Ge Ge For the nuclear models, consider three active schools of thoughts: • 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 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) C. Nones, talk at. DBD06 Workshop, ILIAS-WG1, Valencia, April 2006

  31. Present limit Final sensitivity 7x1024 y 3x1024 y 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 Nuclear models QRPA Tuebingen et al. Shell model QRPA Jyväskylä et al. T1/2 x 1024 y for 130Te

  32. ~50 meV ~20 meV Inverted hierarchy band CUORE and the inverted hierarchy region Mbb S. Pascoli, S.T. Petcov Quasi-degenarate Inverted hierarchy Normal hierarchy Lightest neutrino mass

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

  34. 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

  35. Conclusions • Bolometers represent a well established technique, very competitive for • neutrinoless DBD search • Cuoricino is presently the most sensitive 0n 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

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