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Present status of CUORE / CUORICINO

Present status of CUORE / CUORICINO. 3rd IDEA meeting, Orsay, April 14 – 15, 2005. Andrea Giuliani. Università dell’Insubria and INFN Milano. The CUORE collaboration. 14 institutions – 4 countries - ~ 60 physicists. This technique has been dominating

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Present status of CUORE / CUORICINO

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  1. Present statusof CUORE / CUORICINO 3rd IDEA meeting, Orsay, April 14 – 15, 2005 Andrea Giuliani Università dell’Insubria and INFN Milano

  2. The CUORE collaboration 14 institutions – 4 countries - ~ 60 physicists

  3. This technique has been dominating the field for decades and is still one of the most promising for the future E. Fiorini – 60s  Ge diodes + 76Ge high energy resolution 3.5 keV FWHM reasonable candidate (Q=2039 keV) The bolometric technique for the study of DBD was proposed by E. Fiorini and T.O. Niinikoski in 1983  Bolometers + 130Te, .... good candidate (Q=2528 keV) high energy resolution 4 keV FWHM exceptionally 7 keV FWHM routinely other good or excellent candidates can be studied The (source  detector) technique This is the most sensitive experimental technique up to now With high energy resolution, it can be realized in two ways:

  4. b = 0 b  0 live time energy resolution source mass F MT F (MT / b DE)1/2 importance of the nuclide choice (but large uncertainty due to nuclear physics) 1/4 b DE 1 sensitivity to mee (F/Q |Mnucl|2)1/2  |Mnucl| Q1/2 MT Experimental sensitivity to 0n-DBD sensitivity F lifetime corresponding to the minimum detectable number of events over background at a given (1 s) confidence level b: specific background coefficient [counts/(keV kg y)]

  5. excellent feature for future reasonable-cost expansion of Double Beta Decay experiments C large phase space, lower background (clean window between full energy and Compton edge of 208Tl photons) 2615 2360 • high natural isotopic abundance (I.A. = 33.87 %) • high transition energy (Q = 2528.8 ± 1.3 keV) • encouraging theoretical calculations for 0n-DBD lifetime 2528 E mee 0.1 eV  t  1026 y 0n-DBD half-life (y) for mee = 0.1 eV (different calculations) Comparison with other candidates: Isotopic abundance (%) Transition energy (MeV) 5 40 1030 4 20 1027 3 0 1024 2 48Ca 76Ge 82Se 96Zr 100Mo 116Cd 130Te 136Xe 150Nd 48Ca 76Ge 82Se 96Zr 100Mo 116Cd 130Te 136Xe 150Nd 48Ca 76Ge 82Se 96Zr 100Mo 116Cd 130Te 136Xe 150Nd Properties of 130Te as a DBD emitter 130Te presents several nice features:

  6. All the energy deposited is measured  (bulk and surface bkg are ) The detector is FULLY SENSITIVE  (no dead layer) SOURCE = DETECTOR technique  (Source mass optimization) Very good energy resolution  Signal: DT = E/C Time constant = C/G (no 2n background) Wide material choice   (Phase 2 or 3?) LOWTEMPERATURES Some basic concepts on bolometers

  7. The TeO2 bolometers history: Moore’s Law Cuoricino MASS (Kg) Mi-DBD 4 detectors array 340 g 73 g 1985 1990 1995 2000 2005 2010 2015 Year CUORE

  8. CUORE / CUORICINO in Gran Sasso Labs CUORE R&D (Hall C) CUORE location (Hall A) Cuoricino (Hall A)

  9. 11 modules, 4 detector (790 g) each 2modules,9detector (330 g) each CUORICINO = tower of ~ 5  1025130Te nuclei M = ~ 40.7 kg This detector is completely surrounded by active materials. Useful for BKG origin models The CUORICINO set-up I run : 29 5x5x5 15 3x3x6 TOTAL130Te MASS 59 moles II run : 40 5x5x5 17 3x3x6 TOTAL 130Te MASS 83 moles

  10. Coldest point Cold finger CUORICINO Tower Roman lead shield CUORICINO shieldings

  11. 330g 790g CUORICINO results (1) Calibration (U + Th) sum spectrum of all the detectors average FWHM @ 2.6 MeV (during calibrations) 7.5  2.9 keV (790g) – 9.6  3.5 keV (330g) The best energy resolution (790 g) @ 2615 keV is 3.9 keV

  12. CUORICINO results (2) Updated to 6th Dec ’04 Background sum spectrum of all the big detectors in the DBD region MT = 10.8 kg y (big + small, natural) BKG = 0.18 ± 0.01 counts/ (kev kg y) FWHM (790g) 7.8 keV (330g) 12.3 keV T1/20n (130Te) > 1.8 x 1024 y (90% c.l.) mee < 0.2 – 1.1 eV

  13. Staudt et al. Elliot Vogel 2002 11.3 3.0 20.0 4.6 3.5 4.2 T1/2 (76Ge)/T ½(130Te) expected T ½(130Te) (units: 1024 y) limit: > 1.8 1.06 4.0 0.6 2.6 3.4 2.8 CUORICINO prospects (1) Is CUORICINO able to scrutinize the HM experiment claim? mee = 50 meV – half life for different nuclei and models [1026 y]

  14. Staudt et al. 141 37 251 57 44 53 S/N ratio (s) 7.4 2.0 13 3.0 2.3 2.8 good chance to have a positive indication BUT: cannot falsify HM if no signal is seen CUORICINO prospects (2) Expected event numberin 3 y in a 16 keV energy window (2 FWHM) 1 s BKG fluctuation = (0.19 * 16 * 40.7 * 3)0.5 = 19 (to be compared with 28.75 events of the HM claim, with a BKG level which is 0.11 / 0.19 = 0.6 lower in HM and with an energy resolution which is 2.5 x better in HM)

  15. CUOREis a closely packed array of 988 detectors(cylindrical option) M = 741 kg Each tower is a CUORICINO-like detector CUORE 19 towers with 13 planes of 4 crystals each Special dilution refrigerator

  16. Montecarlo simulations of the background show that b ~ 0.001 counts / (keV kg y) can be reached with the present bulk contamination of det. materials The problem is the surface background (beta - alpha, energy-degraded):  it MUST be reduced by a factor 40 10 y sensitivity with pessimistic b = 0.01 counts/(keV kg y) G = 10 keV 10 y sensitivity with optimistic b = 0.001 counts/(keV kg y) G = 5 keV F0n = 2.1 ´ 1026 y F0n = 9.2 ´ 1026 y mee < 0.01 – 0.05 eV mee < 0.02 – 0.1 eV mee < 7 – 38 meV enriched CUORE CUORE background and sensitivity

  17. Excluded since adding B-polyethilene shield had no effect The alpha continuum extends down to the DBD region CUORICINO ~ 0.2 counts/ keV kg y CUORICINO background model (1) PRELIMINARY ! We have identified 4 possible sources for the residual BKG in the DBD region: • Neutrons • 208Tl multi-compton events • b anda from TeO2 surface • b anda from Cu(or other mat.) surfaces facing the crystals

  18. 208Tl S. E. 214Bi 60Co 208Tl multi-compton in 0n-DBD region To understand our background we NEED surface contaminations

  19. Fix the U and Th crystal cont. levels and depth through MC reconstruction of the COINCIDENCE spectrum in the spectral region 2.5 – 6.5 MeV  Contamination depth in crystals  1 mm CUORICINO background model (2) In the ANTICOINCIDENCE bkg spectrum Crystal bulkcontaminations determine gaussian peaks at the Q-value of the decay Surfacecontaminations determine peaksat the a energy, with tails (shape depending on contamination depth) In the COINCIDENCE spectrum only CRYSTAL SURFACE contam. contribute

  20. Reconstruct the ANTICOINC. spectrum in the spectral region 2.5 – 6.5 MeV problem in this region INGREDIENTS: • 210Po bulk contamination of the crystals (5.4 MeV gauss. Peak, decaying) • 210Pb surface contamination of the Cu + crystal (5.3+5.4 MeV constant peak) • U + Th crystal surface contam. (fixed through the coincidence spectrum) CUORICINO background model (3)

  21. Introduce 238U or 232Th surface contamination level and depth profile due to the Cu structure facing the detectors bulk crystal cont. contamination depth: ~ 5 mm in agreement with direct measurement on Cu CUORICINO background model (4) surface contamination level: ~ 1 ng/g vs bulk c.l. : < 1 (0.1) pg/g for Cu (TeO2)

  22. CUORICINO background origin Rejectable events (by anticoincidence) TeO2 crystal TeO2 crystal Dangerous events

  23. Bulk contamination of Cu and TeO2 < 0.004 counts / kev kg y • Contamination in the cryostat shields can be made negligible by the granular structure and more Pb • Surface contamination as it is  0.04 counts / kev kg y (reduction due to decrease of Cu area and different geometry, but not enough) Crystals and Copper cleaning procedure by chemical etching and surface passivation under development The CUORE background Full Montecarlo simulation on the basis of the CUORICINO and Mi DBD background analysis A reduction by a factor 10 in Cu surface contamination and by a factor 4 in TeO2 surface contamination would correspond to a FULL success of CUORE

  24. New Cleaning procedure Crystal Copper Crystal etching (Nitric acid) • Etching • Electro polishing • Passivation procedure Radio-clean materials Lapping with clean powder (2μ SiO2) New assembling procedure with selected clean materials Surface Contamination Reduction

  25. Energydeposited in the TeO2 crystal (DBD-like event) “classical” pulse “classical” pulse “classical” pulse fast high saturated pulse Energy deposited in the Ge crystal (degraded alpha event) Development of surface-sensitive bolometers Use a thin Ge (or TeO2) crystal to make a composite bolometer

  26. Tests are in progress Suitable compounds to be searched for CUORE for multi-isotope search Calorimetric technique is powerful, but provides limited information In case of discovery or hints for discovery, cross checks are mandatory • remove doubts about unexplained lines of other origin • test nuclear models • reduce systematic uncertainty on the relevant parameters, like mee Already tested bolometrically As good as TeO2 CaF2, Ge, PbMoO4, CdWO4 Other compounds under test

  27. Conclusions • Cuoricino experiment may confirm the HM claim soon,provided the nuclear matrix elements are reasonably favourable • A full Montecarlo simulation for CUORE has been developed, on the basis of the CUORICINO and Mi DBD background analysis • An intense R&D work is going on to reduce the BKG, in order to permit to CUORE experiment to investigate the inverse hierarchy region of the neutrino mass pattern

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