Search for Neutrinoless Double- Beta Decay with CUORE

Transcription

1 Search for Neutrinoless Double- Beta Decay with CUORE Kyungeun E. Lim (on behalf of the CUORE collaboration) Jan. 14, 2014, WIDG Seminar, Yale University

2 What we (don t) know about Neutrinos Neutrino Mass Splitting m 2 m 2 ν e ν µ mev ν τ Degenerate m 3 2 solar~7 5 ev 2 m 2 2 m 1 2 m 2 2 m 1 2 atmospheric ~2 3 ev 2 atmospheric solar~7 5 ev 2 ~2 3 ev 2 m 3 2?? 0 Normal Hierarchy Inverted Hierarchy Rep. Prog. Phys. 76, (2013) 0 Is the neutrino its own antiparticle?!2

3 Outline Neutrinoless double-beta decay search CUORE : An array of TeO2 bolometers CUORE-0 : Validation of CUORE and more Summary!3

4 Neutrino(less) double-beta decay 2νββ decay 0νββ decay Nuclear Mass Even Mass Number N, Z odd β forbidden ββ ββ + N, Z even - Allowed in SM" - Observed in several nuclei " (T1/2 2ν ~ yr) Z 1 Z Z+1 Z+2 Atomic Number - Beyond SM (Lepton number violating process)" - Hypothetical process only if and m ν > 0 ν = ν Z 2 Observation of 0νββ decay 1. will establish that neutrinos are Majorana Particles ( ν = ν )" 2. will provide indirect info of the ν mass " 3. may provide info about the mass hierarchy!4

5 Signature of 0νββ Decay ββ summed e - energy spectrum 2νββ 0νββ ( Assumes BR 0ν/2ν = 1% and detector energy resolution is 2%) Look for peak in the detector at the Q-value of decay." Good energy resolution of a detector suppresses intrinsic background from 2νββ decay.!5

6 Signature of 0νββ Decay ββ summed e - energy spectrum 2νββ 0νββ ( Assumes BR 0ν/2ν = 1% and detector energy resolution is 2%) unavoidable background Q ΔE 6 unavoidable background" sum electron energy / Q E/Q ββ Look for peak in the detector at the Q-value of decay." Good energy resolution of a detector suppresses intrinsic background from 2νββ decay.!6

7 Search for 0νββ Decay Decay rate: (T1/2) 0 1 = G 0 (Q, Z) M 0 2 hm i 2 m 2 e Well defined T1/2 0ν 0νββ half-life G 0ν (Q,Z) phase space factor (/ Q 5 ) M 0ν m ββ me Nuclear Matrix Element (NME) effective ββ neutrino mass electron mass Difficult to calculate - Probes absolute mass scale" - Sensitive to hierarchy!7

8 Search for 0νββ Decay Decay rate: (T1/2) 0 1 = G 0 (Q, Z) M 0 2 hm i 2 T1/2 0ν sensitivity / a m 2 e r M t b E T1/2 0ν 0νββ half-life G 0ν (Q,Z) phase space factor (/ Q 5 ) M 0ν m ββ me Nuclear Matrix Element (NME) effective ββ neutrino mass electron mass a isotopic abundance of source ε detection efficiency M total detector mass b background rate /mass/energy t exposure time δe energy resolution (spectral width)!8

9 Search for 0νββ Decay Decay rate: (T1/2) 0 1 = G 0 (Q, Z) M 0 2 hm i 2 T1/2 0ν sensitivity / a m 2 e r M t b E Detector Building Strategies High Q-value" Large total mass" High isotopic abundance" Ultra-low background" Good energy resolution" NME T1/2 0ν 0νββ half-life G 0ν (Q,Z) phase space factor (/ Q 5 ) M 0ν m ββ me a ε M b t δe Nuclear Matrix Element (NME) effective ββ neutrino mass electron mass isotopic abundance of source detection efficiency total detector mass background rate /mass/energy exposure time energy resolution (spectral width)!9

10 Search for 0νββ Decay (T1/2) 0 1 = G 0 (Q, Z) M 0 2 hm i 2 T1/2 0ν sensitivity / a m 2 e r M t b E Detector Building Strategies High Q-value" Large total mass" High isotopic abundance" Ultra-low background" Good energy resolution" NME Z, number of protons Z=8 Z=20 Z=28 N=8 T1/2 0ν 0νββ half-life G 0ν (Q,Z) a ε M 0ν m ββ me M b t δe N=28 N=20 Z=50 phase space factor Nuclear Matrix Element (NME) effective ββ neutrino mass electron mass (/ Q 5 ) isotopic abundance of source detection efficiency total detector mass Z=82 background rate /mass/energy exposure time N=126 energy resolution (spectral width) N=50 130Te N, number of neutrons!

11 130 Te for 0νββ Decay Q-value [kev] Ca 96 Zr Sn 150 Nd 82 Se Cd 76 Ge 0 Mo 136 Xe 128 Te 130 Te for m ββ = 50 mev 1/2 Expected T IBM QRPA-T QRPA-J ISM PHFB GCM Isotopic Abundance [atomic %] 130 Te + thermal detector w/ excellent energy resolution is appealing for the 0νββ decay detection. dn/de 48 Ca 16 CUORE-0 Preliminary Ge kev 82 Se 96 Zr 0 Mo 116 Cd CUORE-0 Calibration Spectrum 228 Ac" (911) 228 Ac" (969) 124 Sn 128 Te 130 Te 208 Tl" (2615) 136 Xe (FWHM:" ~5 kev) 0νββ 150 Nd 0 Sep Energy [kev]!11

12 TeO2 Bolometers Thermal Bath! L! TeO 2! H T! Absorber" (TeO2) Heater Thermistor" (NTD-Ge) Thermal coupling" (PTFE + gold wires) Measure energy deposition through temperature rise. Voltage [mv] ΔE - Crystal absorber: " E! T - Biased T sensor:" T! V - Thermal coupling: T0 ~ 13 mk Time [s]!12

13 Outline Neutrinoless double-beta decay search CUORE : An array of TeO2 bolometers CUORE-0 : Validation of CUORE and more Summary!13

14 The CUORE 0νββ Search CUORE: Cryogenic Underground Observatory for Rare Events Cuoricino" ( ) CUORE-0" ( ) CUORE" ( ) Achieved (2008) Projected (2015) Projected (2020) hm i 90% C.L. = mev hm i 90% C.L. = mev hm i 90% C.L. = mev!14

15 CUORE Collaboration (Oct. 31, LNGS)!15

16 CUORE Yale Group Karsten Heeger (faculty, PI)" Reina Maruyama (faculty)" Tom Wise (research scientist)" Kyungeun Lim (postdoc)" Jeremy Cushman (grad) Development of the CUORE detector system" Calibration of CUORE" Development of CUORE muon tagging system" Commissioning of CUORE cryostat" CUORE and CUORE-0 analysis!16

17 CUORE at LNGS!17

18 4.52&62$"2*/$7&'( 8 &7) 9: 3 CUORE at LNGS :; > :; : :; < :; - '""$%&'("$")*&+,$")&"3./0,1"2$3!18

19 The CUORE Detector Pulse Tube Refrigerator (5) Roman Lead Shield (6 tons) Inner " Lead Shield (0.7 K) (0.07 K) ( mk) (300 K) (40 K) (4 K) Dilution" Refrigerator PE + H3BO3 Shield Outer Lead Shield 988 TeO2 bolometers (19 towers)!19

20 Detector Improvements More bolometers (Self-shielding, more powerful single crystal hit requirement)." More radiopure crystals." Improved copper surface treatment, less of copper." Optimized tower assembly procedure." Radiopure materials + Roman lead shield ( < 4mBq/kg 2 Pb) for cryostat." Separated DU suspension from crystal tower suspension. Cuoricino CUORE-0 CUORE 130 Te mass [kg] Background /- 20 kev E resolution (FWHM) 2615 kev ~ <m ββ > 90% C.L !20

21 Mass: from a few kg to a ton scale Production of CUORE crystals started at SICASS in China in 2008." Transported via ship to avoid cosmogenic activation." All the crystals are procured." Stored in a dedicated storage area underground. CUORE!21

22 TeO2 Crystals Crystal cutting, wrapping is done in the clean room in SICASS." Visual Inspection (Free of precipitates/cracks/scratches)" Randomly select 4 crystals from each production batch and test bolometric performance (CUORE Crystal Validation Runs, CCVR) CCVR 1-9 Avg: 5.1 +/- 2.1 kev!22

23 CUORE Crystal Validation Runs CCVR also serves as radioactive contamination measurements of the crystals. Counts/(5 kev) 5 4 Anti-Coincidence - M1 Anti-Coincidence - M Energy [kev] Astropart. Phys. 35, 839 (2012)!23

24 Reduction of Copper Surface Contamination Three Tower Test (TTT) Astropart. Phys. 45, 13 (2013) - T1: Polyethylene wrapped" - T2: Chemical etching and cleaning" - T3: Tumbling, Electropolishing, Chemical etching, " and Magnetron plasma etching (TECM) cleaning - Best results (T1) is 0.052±0.008 c/kev/kg/yr in the 2.7 to 3.9 MeV range." - T3 is comparable to T1." - x2 less value compared to that of Cuoricino. 190 Pt!24

25 Detector Assembly Cryostat! Gluing! Storage! Assembly! Crystals are prepared & assembled into towers inside N2-fluxed glove boxes in clean room.!25

26 Detector Assembly Gluing machine Tower garage Cryostat! Storage! Gluing! Assembly! Wire bonding Mechanical assembly!26

27 CUORE Cryogenic System Custom, cryogen-free dilution refrigerator (minimum maintenance and dead time)" Separation of detector suspension from the cryostat suspension" Total mass: ~ 20 tons" Internal Roman lead shield : 6 cm thick doi:.38/news (nature) arxiv: Calibration system!27

28 CUORE Calibration System A string with source capsules move from the top of the cryostat at 300K to the bolometer array at ~ 13mK." The source capsules are mechanically squeezed by a thermalizer and cooled down to 4K. 9mm recess Block pushing surface " L = 50mm 9mm recess Cooled down source capsules arrive near the bolometers to irradiate the detector.!28

29 Cryostat Installation!29

30 Cold Test Results Pulse tube refrigerators successfully cooled down the cryostat as low as 3.5 K in July 2013." Mechanical/thermal performance of the calibration system was verified. 300K 200K 3 (of 5) PTR running 250 hr cold down 9 8 Cooling Time Si-Diode inside Thermalizer 0K 0K Time Temperature [K] T sensor on " Moving Block Elapsed Time [s]!30

31 Dilution Refrigerator Custom dilution refrigerator ordered from Leiden Cryogenic - Base temperature was measured to be as low as 5.6 mk" - More than 5 μw of cooling mk Mixing&Chamber&Temperature&[mK]& 15" 13" 11" 9" 7" S-ll"0"mW"HEX"0"uW" S-ll"0"mW"HEX"62"uW" S-ll"0"mW"HEX"125"uW" S-ll"0"mW"HEX"187"uW" S-ll"4"mW"HEX"0"uW" S-ll"4"mW"HEX"62"uW" S-ll"4"mW"HEX"125"uW" S-ll"4"mW"HEX"187"uW" S-ll"8"mW"HEX"0"uW" S-ll"8"mW"HEX"62"uW" S-ll"8"mW"HEX"125"uW" S-ll"8"mW"HEX"187"uW" 5" 0" 2" 4" 6" 8" " MC&Power&[µW]&!31

32 External Shields Installation is ongoing - 18 cm of Polyethylene" - 2 cm of boric acid (H3BO3)" - 25 cm of Pb" - Steel container for N2 flushing!32

33 Progress towards CUORE Cryostat assembled, commissioning, passed 4 K Test. Detector calibration system well underway. - 9 out of 19 towers completed. " - Installation in the cryostat is anticipated in this year. (0.7 K) (0.07 K) ( mk) (300 K) (40 K) (4 K) Dilution Refrigerator reached 5 mk for the commissioning test. External shields installation is ongoing CUORE-0, the first tower from CUORE assembly line is running in the Cuoricino cryostat.!33

34 Outline Neutrinoless double-beta decay CUORE : An array of TeO2 bolometers CUORE-0 : Validation of CUORE and more Summary!34

35 CUORE-0 The first CUORE-like tower hosted in old Cuoricino cryostat." Validated new cleaning and assembly procedures for CUORE." Will surpass Cuoricino sensitivity before CUORE starts running." 52 (13 x 4) crystals, 39 kg of TeO2 (11 kg of 130 Te), 4 kg of copper structure." Taking 0νββ decay data since March 2013.!35

36 CUORE-0 The first CUORE-like tower hosted in old Cuoricino cryostat." Validated new cleaning and assembly procedures for CUORE." Will surpass Cuoricino sensitivity before CUORE starts running." 52 (13 x 4) crystals, 39 kg of TeO2 (11 kg of 130 Te), 4 kg of copper structure." Taking 0νββ decay data since March 2013.!36

37 CUORE-0: Calibration dn/de 3 16 CUORE-0 Preliminary CUORE-0 Calibration Spectrum 232 Th source 00 Counts/keV CUORE-0 Calibration Spectrum CUORE-0 Preliminary 0 Sep # of bolometers Energy [kev] FWHM: 6.3keV σ: 2.2keV Energy [kev] Sep !37

38 CUORE-0: Background counts/kev/kg/y 2 1 CUORE-0 Preliminary Cuoricino Cuore Sep Energy [kev] γ background (from 232 Th) was not reduced since the cryostat remained the same. " γ background (from 238 U) was reduced by a factor of 2 due to better radon control." α background from copper surface and crystal surface was reduced by a factor of 6 thanks to the new detector surface treatment.!38

39 CUORE-0: Background counts/kev/kg/y 1-1 0νββ 208 Tl 190 Pt Cuoricino Cuore Energy [kev] Avg. flat bkg. [counts/kev/kg/y] signal eff. [%] 0νββ region kev (detector+cuts) Cuoricino ± ± ±1.1 CUORE ± ± ±1.9!39

40 Blinding 0νββ Region Events / ( 5 kev ) Co Salted Peak NOT NDBD Fake Peak! Event Rate [counts/kev/kg/y] Energy [kev] Region of Interest was blinded by salting : exchange a small (and blinded) fraction of the events in 208 Tl peak with events in the 0νββ region to produce fake peak. cnts/kev Real Data Salted Data (f=.15) Simulated Salted CUORE-0 Data Data Salting Energy (kev)!40

41 CUORE-0 Sensitivity Isotope Exposure [kg y] [y] 90% C.L. Sensitivity 0ν 1/2 24 (2013-Nov) CUORE-0 Projected Cuoricino limit T Live time [y] Expected to surpass Cuoricino limit w/ 1.1 year of live time.!41

42 CUORE Sensitivity Sensitivity [y] 1σ 26 Cuoricino CUORE-0 - bkg: 0.05 cts/(kev kg y) CUORE - bkg: 0.01 cts/(kev kg y) [ev] m ββ CUORE 1-σ sensitivity Cuoricino exclusion 90% C.L. 76 Ge claim Inverted 76 Ge exclusion (GERDA+IGEX+ HdM) 136 Xe exclusion KamLand-ZEN+EXO 0ν 1/2 T 25 Normal Live time [y] [ev] m lightest 1σ sensitivity T1/2 0νββ =1.6 x 26 yr (Effective Majorana mass 47-0 mev). - Assuming bg rate of 0.01 cts/(kev kg y) and 5 kev FWHM ROI resolution." - 5 years of live time. arxiv: !42

43 Beyond CUORE Light Detector - Trailing Edge Sensor" - Microwave Kinetic Inductance Detectors Light" (Cerenkov emission" /scintillation) Thermometer Energy " Deposit Enrichment of the crystal (more 130 Te)" Particle discrimination by simultaneously measuring heat/light. (Scintillating)" Bolometer 130 TeO2, Zn 82 Se, 116 CdWO4," Zn 0 MoO4!43

44 background Beyond CUORE [kev] E L <E L > [kev] Astropart. Th Phys. calibration 35, 558 (2012) TeO β/γ α Energy[keV] Astropart. Phys. 34, 143 (20) 50 Light [kev] β/γ 116 CdWO4 α Enrichment of the isotope" Energy (Heat) [kev] Particle discrimination by simultaneously measuring heat/light !44

45 Summary!!!!!! TeO 2 bolometers offer a well-established and competitive technique to search for 0νββ decay. " CUORE, the largest cryogenic detector using TeO 2 bolometers with 206 kg of 130 Te mass, is under construction." Significant efforts have been made to reach very low background goals of CUORE. " CUORE-0, the first CUORE-like tower currently operating at LNGS, demonstrated the success of background mitigation, and will surpass the sensitivity of a predecessor experiment in the coming year." CUORE Yale group is active on the development of calibration system, muon tagging system, calibration/commissioning of CUORE, and CUORE-0 data analysis." CUORE will start to take data next year (2015)." Various R&D projects are ongoing for searches beyond CUORE.!45