Background Rejection for CANDLES System Saori Umehara - PowerPoint PPT Presentation

Background Rejection for CANDLES System Saori Umehara umehara@km.phys.sci.osaka-u.ac.jp CANDLES Collaboration Department of Physics, Osaka University T. Kishimoto, I. Ogawa, K. Matsuoka, R. Hazama, S. Yoshida, K. Ichihara, Y. Hirano, D. Yokoyama, K. Mukaida, A. Yanagisawa Faculty of Integrated Arts and Science, The University of Tokushima K. Fushimi Faculty of Culture and Education, Saga University H. Ohsumi

Outline CANDLES for Double Beta Decay of 48 Ca Design Concept of CANDLES for Background Rejection Design Concept of CANDLES for Background Rejection π Active Shield 4 π Active Shield 4 Expected Background Expected Background Internal Background Internal Background Background Rejection & Reduction Background Rejection & Reduction High Purity CaF 2 Crystal High Purity CaF 2 Crystal Sequential Pulse Rejection Sequential Pulse Rejection α and γ rays Pulse Shape Discrimination between α and γ rays Pulse Shape Discrimination between Position Correlated Background Rejection Position Correlated Background Rejection Summary Summary Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Design Concepts of CANDLES CANDLES CANDLES CAlcium fluoride for studies of Neutrino and Dark matrters by Low Energy Spectrometer Undoped CaF CaF 2 Scintillator (CaF (CaF 2 (Pure)) Undoped 2 Scintillator 2 (Pure)) Double Beta Decay Source 48 Ca (Q ββ =4.27MeV) Peak Emission at UV Region (280nm) Liquid Scintillator ↓ (Veto Counter) Wave Length Shifter Liquid Scintillator Scintillator Liquid Wave Length Shifter 4 π Active Shield Large Photomultiplier Tube Large Photomultiplier Tube Signals from both scintillators are detected simultaneously Active Shielding Technique Active Shielding Technique CaF 2 (Pure) Different Time Constants : ～ 1 µ sec Buffer Oil CaF 2 (pure) Liquid Scintillator : a few 10 nsec Saori Umehara, 20th Sep. 2005, US-Japan Seminar Large PMT

Active Shielding Technique (Pulse Shape) Setup π Active Shield Concept of 4 π Active Shield Concept of 4 Acrylic Case :20 × 20 × 20cm 3 and Performance Test and Performance Test 5inch PMT Pulse Shape of Signals from CaF 2 and Liquid Scintillators Liquid Scintillator CaF 2 (pure) Typical Pulse Shape of Each Scintillators by 100MHz FADC :10 × 10 × 10cm Pulse Height(10mV/ch) 90 CaF 2 (pure) CaF 2 (pure) Liquid Scintillator 60 140 80 +Liquid Scintillator 120 50 70 60 100 40 50 80 30 40 Liquid Scintillator 60 30 20 CaF 2 (pure) 40 20 10 20 10 0 0 0 50 100 150 200 250 300 350 400 50 100 150 200 250 300 350 400 50 100 150 200 250 300 350 400 Time(10ns/ch) Time(10ns/ch) Time(10ns/ch) Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Active Shielding Technique π Active Shield and Performance Test Concept of 4 π Active Shield and Performance Test Concept of 4 Dual Gate Technique Charge of Partial ADC Gate Ratio = Charge of Full ADC Gate Ratio Partial/Full 1 1 Ratio Partial/Full 80nsec 2νββ 0νββ Partial ADC Gate Energy 2400 ～ 2600keV Liq. Scintillator 4 µ sec Full ADC Gate γ -ray 0.8 0.8 Liquid 0.6 Liquid Scintillator 0.6 Event Scintillator CaF 2 (pure) 0.4 0.4 β -ray Clear Discrimination 0.2 CaF 2 (pure) Event 0.2 CaF 2 (pure) 0 0 100 80 60 40 20 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 Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Expected Background in CANDLES Background Studies with CaF 2 (Eu) System External Background External Background (ELEGANT VI) experimental Data Counts(/20keV) 2 νββ 0 νββ Window Strongly Suppressed Strongly Suppressed 10 2 48 Ca(4.27MeV) Because of High Q Q ββ of 48 Ca(4.27MeV) Because of High ββ of 212 Bi π Active Shielding System 4 π 4 Active Shielding System 10 214 Bi 1 208 Tl -1 10 Remaining Background . . .The Only Decays Remaining Background . . .The Only Decays -2 10 2000 2500 3000 3500 4000 4500 5000 νββ Decay Event 2 νββ Energy(keV) Decay Event 2 Simulation Improve Energy Resolution 212 Bi, 214 Bi and 208 Tl ; Natural Radioactivities Natural Radioactivities in CaF in CaF 2 2 (pure) Crystal (pure) Crystal Natural Radioactivities Radioactivities Natural Improve Purity of CaF 2 in CaF 2 (Eu) Crystal in CaF 2 (Eu) Crystal Rejection by Offline Analyses Serious Background Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Light Propagation in CANDLES Standard γ Source Energy Resolution with Prototype Detector Energy Resolution with Prototype Detector CaF 2 Crystal (CANDLES I) (CANDLES I) (10cm Cube) CaF 2 (pure) (280nm Peak Emission) Liquid Scintillator ; Wave Length Shifter PMT ; 5inch × 4 modules PMT Liquid Scintillator PTFE Reflector � Light Collection : ~80% (Borosilicate Glass) (Borosilicate Glass) (Wave Length Shifter) 3000 60 Co (1.17MeV,1.33MeV) Counts 1500 137 Cs (662keV) 2500 1250 2000 1000 9.14%(FWHM) 1500 750 1000 5.91%(FWHM) 500 500 250 0 0 0 200 400 600 800 1000 0 250 500 750 1000 1250 1500 1750 Energy (keV) Energy (keV) Energy Resolution: 9.1%(FWHM) at 662keV =3.4% (FWHM) at 4.27MeV(Q ββ of 48 Ca) Req. for CANDLES III ; 4.0% Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Backgrounds from Natural Radioactivities in Crystals Sequential Pulse Sequential Pulse U-Chain β+α β α 214 Po 238 U 214 Bi 210 Pb T 1/2 = 164 µ sec E max =5.8MeV(U) Q β = 3.27MeV Q α = 7.83MeV 5.3MeV(Th) Th-Chain β α 212 Po Because . . . 232 Th 212 Bi 208 Pb T 1/2 = 0.299 µ sec CaF 2 (pure) Decay Constant 64% stable Q β = 2.25MeV : 900ns Q α = 8.95MeV 208 Tl Event Th-Chain α β 208 Tl 208 Pb E max =5.0MeV 232 Th 212 Bi T 1/2 = 3.05min stable 36% 212 Bi and 208 Tl(T 1/2 =3min) . . . Q α = 6.09MeV Q β = 4.99MeV Space-Time Correlation Cut For Rejection . . . For Rejection . . . Development of High Purity CaF 2 (pure) Crystal Sequential Pulse Rejection by FADC Pulse Shape Discrimination between α and γ rays Space-Time Correlation Cut . . . For 208 Tl Rejection Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Development of High Purity CaF 2 (pure) Crystals Selection of CaF 2 Selection of CaF 2 Powder Powder Growing Process of CaF 2 (pure) Crystals CaF 2 Fused CaF 2 Raw Materials Powder CaCO 3 , HF CaF 2 Crystal Radioactivities in CaF 2 Powder Radioactivities in CaF 2 (pure) Crystal ( α -ray measurement (HPGe measurement) by delayed coincidence) HPGe Measurement . . . For Measurement in CaF 2 Powder Schematic Drawing Sample 170ccGe Pb PL For Measurement OFHC Cu of CaF 2 Powder Pb : HPGe Detector Sensitivity: ～ 3mBq/kg Saori Umehara, 20th Sep. 2005, US-Japan Seminar Ge Detector Preamp

Delayed Coincidence Measurement Delayed Coincidence Measurement . . . Radioactivities in Crystals U-Chain β α 214 Po 238 U 214 Bi 210 Pb Delayed Coincidence = T 1/2 = 164 µ sec Measurement of Q β = 3.27MeV Q α = 7.83MeV Th-Chain α α 216 Po 2 Correlated Event in the Chains 232 Th 220 Rn 212 Pb T 1/2 = 145msec Prompt Decay + Delayed Decay Q β = 2.25MeV Q α = 8.95MeV Typical Energy Spectra(Th-Chain) CaF 2 Crystal Experimental Setup 3 COUNTS(/50keV/kg/day) 31 µ Bq/kg 2.5 2 1.5 220 Rn CaF 2 Crystal 1 216 Po with Reflector 0.5 0 0 500 1000 1500 2000 2500 3000 3500 4000 ENERGY(keV) For Measurement of CaF 2 Crystal : Delayed Coincidence Measurement . . . Sensitivity: ～ 5 µ Bq/kg Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Development of High Purity CaF 2 (pure) Crystals Relation between Radioactivities in Powder and Crystal Check of Radioactivities Relation between Powder and Crystal in many kinds of Powder and Crystals Radioactivities (Arbitrary Unit) Powder Radioactivity (U-chain) 1 Crystal Radioactivity (U-chain) -1 Powder Radioactivity (Th-chain) 10 Crystal Radioactivity (Th-chain) Contaminated -2 10 -3 High Purity Powder 10 High Purity Crystal High Purity -4 10 0 1 2 3 4 A B C Crystal ID Selection of Powder So far . . .CaF 2 (Eu) in ELEGANT VI System :1100 µ Bq/kg U-chain( 214 Bi) :98 µ Bq/kg Th-chain( 220 Rn) U-chain( 214 Bi) : 41 µ Bq/kg (Averaged 42) . . . 1/25 of Previous Crystals Th-chain( 220 Rn) : 21 µ Bq/kg (Averaged 42) . . . 1/5 of Previous Crystals in Progress . . . Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Rejection of Sequential Pulse Sequential Pulse Sequential Pulse T 1/2 = 0.299 µ sec Sequential Pulse Th-Chain β α 212 Bi 212 Po 232 Th Q α =7.8MeV Q β =2.2MeV T 1/2 = 1.1 x 10 10 year 64% Decay Constant of CaF 2 (pure) Prompt Delayed ： 0.9 µ sec Typical Pulse Shape(100MHz FADC) 120 Pules Height(CH/10mV/MeV) Pules Height(CH/10mV/MeV) 100 120 Pules Height(CH/10mV/MeV) 100 100 80 80 80 900ns 60 50ns 60 60 40 Delayed 40 40 20 20 0 20 -10 -5 0 5 10 15 20 Time(10nsec) 0 0 0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300 350 400 Time(10nsec) Time(10nsec) Prompt Background Rejection Efficiency by 100MHz FADC ∆ T > 30ns(3ch) If Fast Sampling FADC . . . ∆ T > 5ns ; Rejection Effi. = 99% Saori Umehara, 20th Sep. 2005, US-Japan Seminar