CANDLES for the study for Double Beta Decay of 48 Ca UMEHARA Saori - PowerPoint PPT Presentation

CANDLES for the study for Double Beta Decay of 48 Ca UMEHARA Saori umehara@rcnp.osaka-u.ac.jp CANDLES collaboration Osaka University, University of Fukui, University of Tokushima, Hiroshima University, Saga University, Kyoto San-gyo University 48 Ca Enrichment Tokyo Institute of Technology, Sophia University

Outline Double beta decay of 48 Ca ELEGANT VI system (previous system) = CaF 2 (Eu) scintillators + CsI(Tl) scintillators system CANDLES System = CaF 2 (pure) scintillators + Liquid scintillator system CANDLES III system at Kamioka underground lab. Pre-measurement for performance test R&D Mass Spectrum of Calcium Summary 40 Ca 42 Ca 43 Ca 44 Ca 46 Ca 48 Ca × 10 × 0.1 × 0.1 × 0.1 × 0.001 × 0.1 UMEHARA Saori, 16 th Nov. 2011, DBD11

Double Beta Decay Neutrino-less double beta decay Double Beta Decay  Neutrino-less double beta decay  Very rare decay T 1/2 > (~10 25 years) nucleus If observed Neutrino → Majorana particle  Lepton number violation Decay rate T 1/2 ∝ 1/m  2 We have studied double beta decay of 48 Ca UMEHARA Saori, 16 th Nov. 2011, DBD11

Double Beta Decay of 48 Ca Why 48 Ca? Higher Q  -value(4.27MeV) . . . 76 Ge(2.0MeV), 100 Mo(3.0MeV), 130 Te(2.5MeV) → Low background because Q  -value is higher than BG E max =2.6MeV( 208 Tl,  -ray) 3.3MeV( 214 Bi,  -ray) We have developed the detector system for no background measurement Double beta decay of 48 Ca by CaF 2 scintillators ELEGANT VI system Scale up CANDLES series

ELEGANT VI ELEGANT VI ELEctron Gamma-ray Neutrino Telescope Schematic drawing of ELEGANT VI CaF 2 (Eu) CaF 2 Scintillator (CaF 2 (Eu)) 23 Crystals(45 × 45 × 45cm 3 :290g) CaF 2 (pure) Source of  Decay : 48 Ca CsI(Tl) (Q  =4.27MeV) veto counters 46 CaF 2 (pure) 38 CsI(Tl) → 4  Active Shield Passive shields for  -ray Cu : 5cm,Pb : 10cm for Neutron LiH LiH+Paraffin :15mm Cd sheet : 0.6mm Cu H 3 BO 3 loaded water Pb Air-tight Box UMEHARA Saori, 16 th Nov. 2011, DBD11

Result of ELEGANT VI Obtained Result Energy Spectra(Jan2003-) COUNTS(/40keV) Q  of 48 Ca Run summary (Measurement for 4 years) 10 2 Date Number of Expected BG Live Time Event ( 212 Bi, 214 Bi, 208 Tl) kg ・ day 10 212 Bi (Sim) Jun1998- 0 1.30 1553 1 Jan2003- 0 0.27 3394 208 Tl (Sim) -1 10 -2 10 No events in 0  Energy Window 3000 3250 3500 3750 4000 4250 4500 4750 5000 Energy(keV) 0  Half-Life of 48 Ca : > 5.8 × 10 22 year ( 90 % C.L.) <m   < (3.5-22) eV ・ 4  active shield is effective for background free measurement. ・ Expected backgrounds are 212 Bi and 208 Tl For higher sensitivity, we need a large amount of 48 Ca.

Design Concepts of CANDLES CANDLES CAlcium fluoride for studies of Neutrino and Dark matrters by Low Energy Spectrometer CaF 2 (pure) scintillator Long attenuation length (>10m@350nm) Double beta decay source 48 Ca (Q bb =4.27MeV) Liquid Scintillator (Veto Counter) Liquid scintillator 4  Active Shield Large photomultiplier tube Signals from both scintillators are detected simultaneously Active Shielding Technique CaF 2 (pure) Different time constants : ～ 1  sec Buffer Oil CaF 2 (pure) Liquid scintillator : a few 10 nsec UMEHARA Saori, 16 th Nov. 2011, DBD11 Large PMT

Active Shielding Technique Setup Concept of 4  Active Shield Liquid Scintillator Acrylic Case and Performance Test :20 × 20 × 20cm 3 PSD between CaF 2 5inch PMT and Liquid Scintillators CaF 2 (pure) Distribution of “charge ratio” :10 × 10 × 10cm 3 80nsec Ratio Partial/Full 1 2  0  Partial ADC Gate Energy 2400 ～ 2600keV Liq. Scintillator 4 µ sec Full ADC Gate γ -ray 0.8 Liquid Liquid Scintillator 0.6 Scintillator Event CaF 2 (pure) Clear Discrimination 0.4 β -ray CaF 2 (pure) Event 0.2 CaF 2 (pure) 0 500 1000 1500 2000 2500 3000 3500 4000 4500 CaF 2 Energy(keV) Clear Discrimination between CaF 2 and Liquid Scintillators . . .Well Act as Veto Counter UMEHARA Saori, 16 th Nov. 2011, DBD11

CANDLES III at Kamioka Lab. CANDLES at Kamioka underground Lab. CANDLES III Kamioka Lab. Map 3m diameter × 4m height (water tank) KamLAND Lab D Super Kamiokande 4m 3m CANDLES CANDLES III

CANDLES III CANDLES at Kamioka underground laboratory CANDLES III CaF 2 scintillator (CaF 2 (pure)) 305 kg (96 modules × 3.2kg)  ~ 1  sec Main detector CaF 2 Scintillators (305kg) Liquid scintillator (LS) 4  Active Shield Volume:2m 3  ~ a few ten nsec Liquid Scintillator Tank(2m 3 ) Large photomultiplier tube 13inch PMT × 48 20inch PMT × 14 for CANDLES III system ・ Characteristic FADC for CaF 2 (long) 13inch and 20inch and LS(short) signals PMTs ・ Selective trigger for CaF 2

FADC for CANDLES For CaF 2 and LS signals . . . And data suppression High sampling rate at the beginning, Low sampling at the ending Typical pulse shape of CaF 2 +LS Pulse Height 800 800 Pulse Height 500MHz at beginning 700 700 500MHz at beginning 600 600 ~16MHz at end 500 500 ~16MHz at end 400 400 300 300 200 200 100 100 0 0 -200 -100 0 100 200 300 400 -400 0 400 800 0 250 500 750 10001250150017502000 0 1000 2000 3000 4000 Time (nsec) Time (nsec) ～ 16MHz × 128 500MHz × 256 LS pulse CaF 2 pulse (Sum at FPGA) Clear Discrimination between CaF 2 and Liquid scintillators ・ Details of PSD will be presented in a poster session by G. Ito Data size is small. ・ 500MHz × 2048data → 500MHz × 256data + 16MHz × 128data

Selective Trigger with normal trigger Ratio Partial/Full 1 Selective trigger for CaF 2 0.8 0.6 by using “threshold for integrated signal” LS CaF 2 0.4 in poster session by M. Saka 0.2 0 500 1000 1500 2000 2500 3000 3500 4000 4500 CaF 2 Energy(keV) at 2600keV Event Distribution with Trigger for CaF 2 No LS Events 1 Ratio Threshold LS Region for integrated signal 80 0.8 well works. at 2600keV 800 Pulse Height 60 0.6 700 CaF 2 + LS 600 500 CaF 2 +LS 40 400 0.4 800 Pulse Height 300 700 200 600 100 500 20 0.2 0 0 250 500 750 1000 1250 1500 1750 2000 CaF 2 400 Time(2nsec) 300 CaF 2 Event 200 0 500 10001500200025003000350040004500 0 100 0 0 0 250 500 750 1000 1250 1500 1750 2000 Energy(keV) Time(2nsec) We obtained . . . ・ High efficiency for CaF 2 Scintillator, Low efficiency for LS

Position Reconstruction Position Reconstruction position(Y) 3 CaF 2 s Counts 225 for events with CaF 2 pulse shapes 200 175 for identification of CaF 2 position 150 125 100 75 position(X) 5 CaF 2 s 50 Counts 25 250 0 -500-400-300-200-100 0 100 200 300 400 500 Position Y 200 position(Z) 6 layers Counts 300 150 250 Lower Upper 200 100 150 50 100 50 0 -500-400-300-200-100 0 100 200 300 400 500 0 -500-400-300-200-100 0 100 200 300 400 500 Position X Position Z We can identify each CaF 2 position. in a poster session by K. Yasuda

Pre-measurement For performance test by standard  source in a poster presentation by H. Kakubata by radioactive contaminations within a reference CaF 2 Delayed  analyses 214 Bi → 214 Po （ U-chain ） 219 Rn → 215 Po （ Ac-chain ） 220 Rn → 216 Po （ Th-chain) U-chain   214 Po 206 Pb  -  decay 238 U 214 Bi T 1/2 = 164  sec stable Q  = 3.27MeV Q  = 7.83MeV UMEHARA Saori, 16 th Nov. 2011, DBD11

Delayed  analysis 214 Bi → 214 Po → 210 Pb decay （ β→α decay in U-chain ） Energy Spectra( ∆ t <300  sec) ∆ t distribution Counts 200 Counts experimental data prompt events 180 simulation 160 10 2 140 120 100 214 Bi Q  80 60 40 20 0 0 500 1000 1500 2000 2500 3000 3500 4000 0 200 400 600 800 1000 Energy(keV) Time(microsec) 200 Counts delayed events experimental data 175 Half-life ： 175 ± 10 μ sec （ 164 μ sec ） fitting 150 energy resolution ：  =4.3% 125 214 Po 100 radioactivity ： 61 ± 9(syst.)mBq/kg 75 （ previous measurement:65mBq/kg ） 50 Expected performances 25 with current CANDLES III were obtained. 0 0 500 1000 1500 2000 2500 3000 3500 4000 Energy(keV)

Expected Background Background Event in CANDLES System Radioactive Contamination within CaF 2 (pure) Background process Th-Chain   208 Pb 212 Po 232 Th 212 Bi stable 64% Q  = 8.95MeV Q  = 2.25MeV T 1/2 = 0.3  sec Pile-up event (Sequential event)  because . . . E max = 5.3MeV CaF 2 (pure) : (Q  = 4.27MeV) time constant ~1  s To reject as the sequential event (background event) ・ identify the “pile-up” shape ・  rays particle identification UMEHARA Saori, 16 th Nov. 2011, DBD11

Sequential Events 212 Bi → 212 Po decay T 1/2 = 0.3  sec Pile-up Th-Chain   212 Bi 212 Po 232 Th Q  =7.8MeV Q  =2.2MeV T 1/2 = 1.1 x 10 10 year 64% Decay Constant of CaF 2 (pure) prompt delayed ： 0.9  sec with small  t Typical pulse shape of sequential events Pulse Height Pulse Height Pulse Height 500 600 500 400 500 400 300 400 200 300 Delayed  100 300 Prompt β 0 200 -100 -50 0 50 100 150 200 200 Time(2nsec) 100 100 0 0 0 250 500 750 1000 1250 1500 1750 2000 0 250 500 750 1000 1250 1500 1750 2000 Time(2nsec) Time(2nsec) Sum-up signal of 62 PMT We can identify the sequential events. Rejection efficiency > 90%