CUORICINO results & status of CUORE

Transcription

1 CUORICINO results & status of CUORE Fabio Bellini Università di Roma La Sapienza & INFN Roma on behalf of the CUORE Collaboration 1st Boulby Underground Science Workshop York, England Oct ,

2 Neutrino-less Double Beta Decay n u d dl W U ek u d ul p el _L νk ν R n dl d u mk k el Uek W ul d u p Neutrino nature chirality flip: m 0 majorana : Lepton number violation Strumia, Vissani Nucl.Phys.B726:294,2005 Degenerate Inverse Absolute mass scale and hierarchy / 2 =G Q, Z M nucl m Direct 2 m = m U ek k Effective neutrino mass 2

3 CUORICINO: the bolometric way Bolometric technique: energy measured as a temperature increase in the detector Homogeneous detector: ββ0ν source absorber (Very) Low temperature calorimeter: basic physics T= E/C low C diamagnetic low T (~ 10mK) : C~T3 ~1010eV/K Thermometer: NTD Ge thermistor R~ R0exp(T0/T)~0.5 T R 0.1 mk/mev 0.1mV/MeV Bonus: no intrinsic limit to σ(e) σ(e) = (KBCT2)0.5 ~10 ev (Not for all) Typical pulse decay time: t ~C/G~102 3 ms 3

4 Why Tellurium? Qββ transition energy Active isotope: 130Te E Transition energy Qββ = ( ±1.99) kev Between the highest natural γ line (208Tl) and Compton edge Nuclear Physics A 729 (2003) 337 Natural abundance C Nuclear matrix element 33.9% low cost Absorber material: TeO2 Rodin nucl th/ Low heat capacity Possibility to grow large crystals Good intrinsic purity 4

5 LNGS Cuor Cu oricino icin o aand nd CUORE CUORE Loca Locattion ion Cu or icin o e x pe r im e n t is in st a lle d in t he Un de r gr oun d N a t ion a l La bor a t or y of Gr a n Sa sso L'Aqu ila I TALY t h e m ou n t a in pr ovidin g a m.w.e. sh ie ld a ga in st cosm ic r a ys CUORE ( hall A) Cuoricino R&D final t est s for CUORE ( hall C) 5

6 CUORICINO: the demonstrator Started on April 2003 long stop between run 1 and run 2 various stops due to maintenance and interferences with Safety upgrade works 11 modules: 4 detector 5x5x5 cm3=790 g each 2 modules 9 detector 3x3x6 cm3=330 g each 4 enriched: 130Te 128Te Total Active mass: TeO2 = 40.7 kg 130 Te = kg Installed in a dilution refrigerator (10 mk) surrounded by: Cu shield Roman Pb inner shield 1.5 cm lateral, 10 cm top&bottom 20 cm Pb external shield Neutron shield: ~10 cm B(10%) polyethylene Anti radon box:nitrogen overpressure 6

7 Calibration spectra: energy resolution Th γ source external to the cryostat: 3 days measurement every month 232 Sum calibration spectra 5x5x5 cm3 3x3x6 cm kev 208Tl γ line 5x5x5 cm3 crystal: FWHM 7.5±2.9 kev 3x3x6 cm3 crystal: FWHM 9.6±3.5 kev 7

8 CUORICINO bkg in the 0νββ region All lines identified all over the whole spectrum: U & Th chains, 40 K, 207Bi, 60Co In 0 region: 30 ± 10% 208Tl ( kev line) via multi Compton events from 232Th in cryostat shields 10 ± 5% from crystals surface 238U and 232Th contamination 50 ± 20% from degraded produced by 238U and 232Th contaminations of mounting structure main candidate the copper surface negligible contribution from 2505 ( ) kev 60Co tail due Cu cosmogenic activation 60 Co Qββ = ( ±1.99) kev 208 Tl 0.18 ±0.01 counts/kev/kg/y 214 Bi 8

9 CUORICINO 0νββ result Total statistics: 8.38 kg 130Te y Bkg (ββ0ν region): 0.18 ±0.01 counts/kev/kg/y FWHM measured on bkg 2.6 MeV ~ 8 kev Detector efficiency: ~86.4% ML fit in kev region flat bkg kev peak peak shape = N gaussian to account for the different measured energy resolutions best fit yields negative effect / C.L. m 0 [ ]ev <m> range from various QRPA calculations: Rodin, Faessler, Simkovic, & Vogel Nucl. Phys. A (2006) Staudt, Kuo & Klapdor Kleingrothaus, PRC (1992) 9

10 In the parameter space KK HM: best 0.24 ev m 0.58 ev m =0.44 ev Klapdor Kleingrothaus et al. Phys. Lett. B 586, CUORICINO: m [ ]ev With 3 years live time: 1 / C.L. m [ ]eV <m> range from various QRPA calculations: Rodin, Faessler, Simkovic, & Vogel Nucl. Phys. A (2006) Staudt, Kuo & Klapdor Kleingrothaus, PRC (1992) 10

11 The Moore's law of TeO2 bolometers Phys. Lett. B 557 (2003)167 Phys. Rev. Lett. 95 (2005) Phys. Lett. B, 335 (1994) 519 Phys. Lett. B, 285 (1992)

12 Cryogenic Underground Observatory Single dilution refrigerator ~10 mk for Rare Events ββ0ν, Cold Dark Matter, Axion searches proposal hep/ph cm 80cm 19 towers 52 detectors each A single tower test (CUORICINO) Closed packed array of 988 TeO2 5x5x5 cm3 crystals 741 kg TeO2 204kg 130Te 12

13 CUORE Housing Basement already completed... the rest is coming 13

14 CUORE sensitivity CUORE ββ0ν sensitivity will depend strongly on the bkg level and detector performance 1st generation exp: proof of technology 2nd generation exp: explore inverted hierarchy CUORE GOAL: test inverse hierarchy: mev Spread due to NME uncertainties: main obstacle to answer ν mass question 14

15 Background reduction Cryostat 232Th bulk contamination contribution reduced by properly shielding in CUORE cryostat + selection of construction materials: bkg= < 10 3 c/kev/kg/y Cosmogenic Cu and Te activation reduced by underground storage of materials Surface contribution: test wih new crystals surface cleaning (etching, lapping with 2 m SiO2clean powder) reduction of a factor 4 test wih new Cu cleaning (etching, electro polishing, passivation) and complete coverage of Cu facing the crystal with ~50 m PET film reduction of ~40% of flat continuum background 15 only Hall C cryostat has different shielding than CUORICINO resulting in higher rates < 2.6 MeV. Possible to study bkg

16 Background reduction The extrapolated contribution to CUORE are Crystal Surface contamination contribution <3 counts/kev/kg/y Copper Surface contamination contribution <5 counts/kev/kg/y New structure with reduced Cu amount is being tested right now MC simulation Cu contribution < 2.5 counts/kev/kg/y still a factor no less than 2.5 to go New passive procedure (plasma cleaning) under test most exp. efforts now concentrated in the reduction of this kind of impurities alternative viable way that guarantees the bkg achievement= Surface Sensitive Bolometers 16

17 CUORE R&D:active bkg rejection Surface sensitive detectors: composite bolometer with a thin Ge, Si, Te02 crystal Bolometer with thin shield absorber and its thermistor classic pulse classic pulse Bolometer with TeO2 crystal absorber and its thermistor classic pulse fast and high pulse The presence of the shield changes the thermal dynamic behavior of the detector giving rise to pulses with different amplitudes and shapes. Different impact points means different pulses on thermistors 17

18 CUORE R&D: active bkg rejection Rise time on slabs 18

19 neutron & background External neutron flux: Φ= n/s/cm2 (measurement E<10MeV + induced neutrons simulation in the rock) Total anti coicidence bkg~10 5 counts/kev/kg/y Muon induced neutrons in the shieldings muon flux Φ = ( ) 10 4 /s/m2, induced neutron flux on detector ± 10-9 n/s/cm2 total anti coincidence bkg= (1.5±0.3) 10 4 counts/kev/kg/y External radiation: 106 /d/cm2 measured with Ge detector bkg= 1.5 counts/kg/kev/y with 24 cm external Pb shield External Pb shield contamination: 100 Bq/kg bkg = 2.4 counts/kg/kev/y Internal shield Roman lead contamination (6cm Pb): 60±17 Bq/kg bkg = counts/kev/kg/y DownRun Pb <22 Bq/kg bkg < counts/kev/kg/y (but 60Co contamination & 27 Bq/kg 210Pb) Cu shield contamination : <12 Bq bkg < counts/kev/kg/y (better for Th contamination.. worse for 60Co contamination and neutron activation) 19

20 Conclusion CUORICINO: The most sensitive ββ0ν decay running experiment: / C.L. m 0 [ ]ev Good chances to confirm KK HM experiment CUORICINO proved the feasibility of CUORE Crucial informations for background identification CUORE: Hut construction already started Intense R&D activity to reduce background and optimize construction and assembly Enrichment or alternative options (48Ca,100Mo,116Cd,150Nd) still open The inverse hierarchy will be explored Start data taking: 1st January

21 CUORE Collaboration Università di Milano Bicocca INFN Sez. di Milano C. Arnaboldi, C. Brofferio, S. Capelli, L. Carbone, M. Clemenza, O. Cremonesi, E. Fiorini, C. Nones, A. Nucciotti, M. Pavan, G. Pessina, S. Pirro, E. Previtali, M. Sisti, L. Torres, L. Zanotti Politecnico di Milano R.Ardito, G. Maier Laboratori Nazionali del Gran Sasso M. Balata, C. Bucci, S. Nisi, C. Zarra Università di Firenze e INFN, Firenze M. Barucci, L. Risegari, G. Ventura University of Zaragoza S. Cebrian, P. Gorla, I.G. Irastorza Università degli Studi dell Insubria, Como A. Giuliani, M. Pedretti, S. Sangiorgio Università di Genova S. Cuneo, S. Di Domizio, A. Giachero, E. Guardincerri, M. Olcese, P. Ottonello, M. Pallavicini Laboratori Nazionali di Legnaro V. Palmieri Università di Roma F. Bellini, C. Cosmelli, I. Dafinei, M. Diemoz, F. Ferroni, C. Gargiulo, E. Longo, S. Morganti, M. Vignati University of California at Berkeley S.J. Freedman, Yu.G. Kolomensky, E.E. Haller University of South Carolina F.T. Avignone III, I. Bandac, R. J. Creswick, H.A. Farach, C. Martinez, C. Rosenfeld Lawrence Berkeley National Laboratory J.W. Beeman, A.R. Smith, N. Xu Lawrence Livermore National Laboratory M.J. Dolinski, E.B. Norman University of California, Los Angeles H. Huang, C. Whitten Jr. University of Wisconsin, Madison K.M. Heeger, R.H. Maruyama California Polytechnic State University T.D. Gutierrez Università di Milano Celoria INFN Sez. di Milano 21 F. Alessandria