LUCIFER Low background Underground Cryogenic Installation For Elusive Rates Marco Vignati INFN Roma NPB 2012, Shenzhen, 24 Sept. 2012
Bolometric searches of 0 ν DBD Bilenky and Giunti, 2012 1 CUORICINO: Current Bound 11kg 130 Te bkg = 0.17 c/keV/kg/y KK evidence - 76 Ge 10 � 1 CUORE: 206kg 130 Te bkg ~ 1 · 10 -2 c/keV/kg/y IS Cosmological Limit |m �� | [eV] 10 � 2 Needs: 1 ton isotope bkg < 10 -3 c/keV/kg/y NS 10 � 3 1 � 2 � 3 � 10 � 4 10 � 4 10 � 3 10 � 2 10 � 1 1 m min [eV] 2
CUORE: the α nightmare • MC: most of the background in CUORICINO is due to degraded α particles which release only a part of their energy in the detector Cu (surface contaminations, mainly in copper). CUORICINO TeO 2 TeO 2 α ’s • TeO 2 bolometers, per se, do not allow to discriminate β and α particles. ‣ α bkg partially reduced by cleaning the detector parts. ‣ β / γ smaller in CUORE thanks also to the self-shielding geometry. 3
Scintillating bolometers • Scintillating crystals can be operated as bolometers. Unfortunately TeO 2 does not scintillate, other compounds must be considered. • The simultaneous read-out of light and thermal signals allows to discriminate the α background thanks to the scintillation yield different from β particles. Light detector Thermistor Bolometer Energy Release 4
Isotope choice . • 0 ν DBD candidates of experimental interest: (arXiv:1201.4916) 76 Ge 130 Te 136 Xe 116 Cd 100 Mo • In general, Q > 2615 keV isotopes 82 Se are preferred because they lie above the natural radioactivity edge. • However the choice has been U and Th dominated so far by technology environmental bkg compromises. 5
Light detectors • Germanium disks (5 cm diameter, 0.1-1 mm thick). • Calibration with a 55 Fe source: 5.9 & 6.5 keV X-rays. ‣ Δ E @ 55 Fe: ~ 130 eV RMS ‣ Δ E @baseline: 100 eV RMS 6
Candidate #1: ZnSe Largest crystal DBD Isotope: 82 Se operated so far: 431g Q-value 2995 [keV] isotopic 9% abundance Light Yield 7-11 [keV/MeV] QF 4 7
ZnSe Light Yield [keV/MeV] 40 • QF > 1 is odd: 35 30 ‣ Observed only in this 25 compound (CdWO 4 20 ZnMoO 4 and other 15 crystals have QF < 1). 10 0 ν DBD ‣ not understood. 5 0 1000 2000 3000 4000 5000 6000 7000 8000 Energy [keVee] Light Decay Time [ms] Light decay-time [ms] β / γ -background 14 13 • Excellent separation α -crystal contamination 12 using light energy and 11 signal shape 10 9 8 7 0 50 100 150 200 250 300 350 400 Detected Light [keV] 8
21 ZnSe: Light-Heat correlation 21 Detected light [keV] Detected light [keV] 20 20 19 19 18 18 17 17 16 16 15 15 14 14 13 13 12 12 2590 2600 2610 2620 2630 2640 2590 2600 2610 2620 2630 2640 Energy [keVee] Decorrelated energy [keVee] counts / 2 keVee Integral Integral 101 101 Integral Integral 101 101 16 12 � � 2 2 / ndf / ndf 4.035 / 13 4.035 / 13 � � 2 2 / ndf / ndf 8.021 / 14 8.021 / 14 14 10.5 10.5 1.5 1.5 13 13 1.9 1.9 10 A A ± ± A A ± ± 12 mean mean mean mean 2614 2614 1.0 1.0 2615 2615 0.6 0.6 ± ± ± ± Δ E@2615 keV: 8 10 � � 7.938 7.938 1.116 1.116 � � 5.741 5.741 0.594 0.594 ± ± ± ± 8 6 13 keV FWHM 6 4 4 2 2 0 0 2590 2600 2610 2620 2630 2640 2590 2600 2610 2620 2630 2640 Energy [keVee] Decorrelated energy [keVee] 9
Plan for a ZnSe array in 2015 • Operation of a tower of 32-40 Zn 82 Se crystals at LNGS. ‣ Option1: use the Cuoricino cryostat in hallA (presently hosting CUORE-0), if CUORE-0 stops in 2015. ‣ Option2: use the cryostat in hallC (presently running the CUORE-0 and LUCIFER R&Ds). Needs cryostat update. Cuoricino cryostat: • Inner shield: - 1cm Roman Pb A ( 210 Pb) < 4 mBq/Kg • External shield: - 20 cm Pb 4 crystals LUCIFER - 10 cm Borated per floor polyethylene • Nitrogen flushing to avoid Rn contamination. 10
ZnSe: schedule 2012 2013 2014 2015 Light detector R&D Thermistors prod. Crystal growth R&D 82 Se prod. (15 kg) Enriched crystals production Array assembly The most crucial part is represented by the crystal growth. The supplier (Ukraine) is presently fine-tuning the complicate procedure (that starts with metal Zn and metal Se). The request of minimizing the 82 Se waste is a complicate issue. The target is to reach > 75 % efficiency. 11
Do we need a μ -veto? 15 Light Yield [keV/MeV] ZnSe data: β / γ 14 1 β / γ event above α 13 the 2615 keV line 12 in 580 hours 11 10 9 ~ 5x10 -2 counts/keV/kg/y 1500 2000 2500 3000 3500 4000 Energy [keVee] • The event includes hits on close detectors (multi-site event) ‣ Multiple γ ’s produced by μ interactions in the materials close to the detector. • Easy to remove in this case, but what if one has one hit only? ‣ Montecarlo simulation under development. 12
Candidate #2: ZnMoO 4 Largest crystal DBD Isotope: 100 Mo operated so far: 330g Q-value 3034 [keV] isotopic 10% abundance Light Yield 1.5 [keV/MeV] QF 0.2 13
LY [keV/MeV] Light Yield [keV/MeV] 2.4 ZnMoO 4 . 2.2 β / γ source 2 1.8 1.6 1.4 0 ν DBD 1.2 Excellent discrimination 1 using the light signal 0.8 0.6 α source 0.4 0.2 500 1000 1500 2000 2500 3000 3500 4000 Energy [keV] TVR [a.u.] Heat signal shape parameter 4 α source 2 0 -2 0 ν DBD Discrimination using the -4 β / γ source shape of the heat signal! -6 -8 -10 -12 Eur. Phys. J. C 72 (2012) 2142 -14 0 500 1000 1500 2000 2500 3000 3500 4000 14 Energy [keV]
ZnMoO 4 counts / 3 keV 70 FWHM= 6.3 keV 90 60 50 Entries 11528 11528 Energy resolution similar 80 40 2.925 to CUORICINO 70 30 20 (2x better than ZnSe) 60 10 0 50 2590 2600 2610 2620 2630 2640 1.153e+04 40 β / γ source 30 Counts / 9 keV 210 Po 20 Entries 2821 2 10 10 Mean 2742 0 RMS 1449 500 1000 1500 2000 2500 source � � Energy [keV] 222 Rn Integral 2821 226 Ra 10 218 Internal contaminations: Po 214 214 Bi � Po 232 Th < 1.4 pg/g 1 3 10 × 1 2 3 4 5 6 7 8 9 10 Energy [keV] 15
Candidate #3: TeO 2 TeO 2 does not scintillate, however MeV β ’s emit Č erenkov light, unlike α ’s [ T. Tabarelli de Fatis, Eur. Phys. J. C 65 (2010) 359] . 800 � dN/d λ [ μ m -1 ] dN/d 700 Simulated Č erenkov emission 600 spectrum from 500 400 1.5 MeV γ in TeO 2 at low 300 temperatures. 200 100 0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 � ( µ m) � � 2 / ndf / ndf 2 3.723 / 5 3.723 / 5 λ [ μ m] Prob Prob 0.5899 0.5899 p0 p0 -3.111e-08 -3.111e-08 ± ± 1.143e-09 1.143e-09 p1 p1 0.0001678 0.0001678 ± ± 4.448e-06 4.448e-06 p2 p2 0.1222 0.1222 ± ± 0.00428 0.00428 Produced Cherenkov light[eV] p3 p3 -10.43 -10.43 0.8393 0.8393 1000 ± ± Cherenkov light (eV) 867 eV 900 800 Simulated emitted 700 600 Č erenkov light as a 0 ν DBD 500 function of β / γ energy. 400 300 200 100 0 0 500 1000 1500 2000 2500 Photon Energy (keV) β / γ energy [keV] 16
Č erenkov from a CUORE crystal 0.4 Light energy [keV] 2 2 / ndf / ndf � � 11.9 / 6 11.9 / 6 0 ν DBD E E [keV] [keV] 360.3 360.3 64.47 64.47 ± ± 0.3 th th Yield [eV/MeV] Yield [eV/MeV] 48.33 48.33 ± ± 2.846 2.846 0.2 e c r u o s γ / β 0.1 0 210 Po- α contamination -0.1 Detected β / γ light: 48 eV/MeV -0.2 105 eV @2.527 MeV -0.3 0 1000 2000 3000 4000 5000 Heat energy [keV] • Detected light not sufficient to discriminate α ’s event by event. ‣ Needs light detector development: light collection, energy resolution. 17
CUORE + Č erenkov + enrichment 18 y] γ bkg. (MC)= 0.001 26 16 DBD sensitivity [10 14 bkg. [counts/keV/kg/y] � 12 0.01 with 90% enr. 0.04 with 90% enr. 10 0.01 8 0.04 6 � 4 68% 0 2 0 0 1 2 3 4 5 6 7 8 Signal/Noise of light detector 18
CUORE + Č erenkov + enrichment 18 y] γ bkg. (MC)= 0.001 Present: S = 105, N = 75 eV 26 16 DBD sensitivity [10 14 bkg. [counts/keV/kg/y] � 12 0.01 with 90% enr. 0.04 with 90% enr. 10 0.01 8 0.04 6 � 4 68% 0 2 0 0 1 2 3 4 5 6 7 8 Signal/Noise of light detector 18
CUORE + Č erenkov + enrichment 18 y] γ bkg. (MC)= 0.001 Present: S = 105, N = 75 eV 26 16 Target DBD sensitivity [10 14 bkg. [counts/keV/kg/y] � 12 0.01 with 90% enr. 0.04 with 90% enr. 10 0.01 8 0.04 6 � 4 68% 0 2 0 0 1 2 3 4 5 6 7 8 Signal/Noise of light detector 18
Overview until 2015 • ZnSe ‣ Target: build a bolometric experiment of ~ 10 kg of 82 Se ‣ Status: Isotope in production, crystal growth under optimization. • ZnMoO 4 ‣ Target: build a bolometric experiment of ~ 10 kg of 100 Mo ‣ Status: MoU with IN2P3 and ITEP in consideration. • TeO 2 ‣ Target: develop light detectors with S/N improved by a factor 4. ‣ Status: KIDs and Neganov-Luke detectors under development. 19
Overview until 2015 • ZnSe baseline ‣ Target: build a bolometric experiment of ~ 10 kg of 82 Se ‣ Status: Isotope in production, crystal growth under optimization. • ZnMoO 4 ‣ Target: build a bolometric experiment of ~ 10 kg of 100 Mo ‣ Status: MoU with IN2P3 and ITEP in consideration. • TeO 2 ‣ Target: develop light detectors with S/N improved by a factor 4. ‣ Status: KIDs and Neganov-Luke detectors under development. 19
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