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CUORE, CUORICINO: Results and perspectives

CUORE, CUORICINO: Results and perspectives. Chiara Brofferio. Università di Milano – Bicocca and INFN, Sez. di Milano. On behalf of the CUORICINO and CUORE Collaborations. Neutrino Telescopes Venice, 22-25 February 2005. All the energy deposited is measured. .

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CUORE, CUORICINO: Results and perspectives

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  1. CUORE, CUORICINO: Results and perspectives Chiara Brofferio Università di Milano – Bicocca and INFN, Sez. di Milano On behalf of the CUORICINO and CUORE Collaborations Neutrino Telescopes Venice, 22-25 February 2005

  2. 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

  3. 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

  4. 330g 790g average FWHM @ 2.6 MeV (during calibrations) 7.5  2.9 keV (790g) – 9.6  3.5 keV (330g) CUORICINO results (1) Calibration (U + Th) sum spectrum of all the detectors The best energy resolution (790 g) @ 2615 keV is 3.9 keV

  5. 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

  6. 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 and the NME models Is CUORICINO able to scrutinize the HM experiment claim? mee = 50 meV – half life for different nuclei and models [1026 y]

  7. 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 discovery potential Expected event numberin 3 y in a 16 keV energy window (2 FWHM) 1 s BKG fluctuation = (0.18 * 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 / 0.18 = 0.6 lower in HM and with an energy resolution which is 2.5 x better in HM)

  8. 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

  9. In the ANTICOINCIDENCE bkg spectrum Crystal bulkcontaminations determine gaussian peaks atthe Q-value of the decay bulk crystal cont. Cu surf. cont. surface crystal cont. CUORICINO background model (2) Surfacecontaminations determine peaksat the a energy, with tails (shape depending on contamination depth) In the COINCIDENCE spectrum only CRYSTAL SURFACE contam. contribute surface contamination level: ~ 1 ng/g vs bulk c.l. : < 1 (0.1) pg/g for Cu (TeO2)

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

  11. CUOREis a closely packed array of 988 detectors(cylindrical option) M = 741 kg 19 towers with 13 planes of 4 crystals each We intend to put heavy lead shieldings INSIDE and OUTSIDE the cryostat 10 tons60 tons Each tower is a CUORICINO-like detector CUORE detector and shieldings

  12. 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  0.074 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 We aim at reaching AT LEAST a reduction by a factor 10 in Cu surface contamination and by a factor 4 in TeO2 surface contamination

  13. 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

  14. Finally: the detector! 8-detectors Array

  15. ANTICOINCIDENCE SPECTRUM Hall C CUORICINO Counts (a.u.) 5000 3000 4000 Energy [keV] Background (3.4-4 MeV): 0.112 +/- 0.018 vs 0.18 +/- 0.02 counts/keV/kg/y We obtained a reduction of a factor 4 (average) on crystal surface contaminations: we reached the milestone of CUORE for this task. 8-detectors vs. Cuoricino

  16. 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

  17. = + Development of prototypes

  18. rise time distribution for Ge pulses FAST surface events SLOW bulk events Preliminary very encouraging results

  19. 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 5 y sensitivity with pessimistic b = 0.01 counts/(keV kg y) G = 10 keV 5 y sensitivity with optimistic b = 0.001 counts/(keV kg y) G = 5 keV F0n = 1.5 ´ 1026 y F0n = 6.5 ´ 1026 y mee < 11 – 57 meV mee < 23 – 118 meV mee < 8 – 45 meV enriched (95%) CUORE CUORE background and sensitivity

  20. 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 • A big 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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