[PPT] - Background Rejection for CANDLES System Saori Umehara PowerPoint Presentation

SLIDE 1

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

SLIDE 2

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Outline

Design Concept of CANDLES for Background Rejection Design Concept of CANDLES for Background Rejection

4 4π π Active Shield Active Shield

Expected Background Expected Background

Internal Background Internal Background

Background Rejection & Reduction Background Rejection & Reduction

High Purity CaF High Purity CaF2

2 Crystal

Crystal Sequential Pulse Rejection Sequential Pulse Rejection Pulse Shape Discrimination between Pulse Shape Discrimination between α α and and γ γ rays rays Position Correlated Background Rejection Position Correlated Background Rejection

Summary Summary

CANDLES for Double Beta Decay of 48Ca

SLIDE 3

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Design Concepts of CANDLES

Undoped Undoped CaF CaF2

2 Scintillator

Scintillator (CaF (CaF2

2(Pure))

(Pure)) Double Beta Decay Source 48Ca (Qββ=4.27MeV) Peak Emission at UV Region (280nm) ↓ Wave Length Shifter Liquid Liquid Scintillator Scintillator Wave Length Shifter 4 π Active Shield Large Photomultiplier Tube Large Photomultiplier Tube Signals from both scintillators are detected simultaneously

CaF2(Pure)

Liquid Scintillator (Veto Counter)

Buffer Oil Large PMT CANDLES CANDLES CAlcium fluoride for studies of Neutrino and Dark matrters by Low Energy Spectrometer

Active Shielding Technique Active Shielding Technique Different Time Constants CaF2(pure) : ～1µsec Liquid Scintillator : a few 10 nsec

SLIDE 4

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Active Shielding Technique (Pulse Shape)

Concept of 4 Concept of 4π π Active Shield Active Shield and Performance Test and Performance Test

Pulse Shape of Signals from CaF2 and Liquid Scintillators

Acrylic Case :20×20×20cm3

Setup

5inch PMT Liquid Scintillator CaF2(pure) :10×10×10cm

10 20 30 40 50 60 50 100 150 200 250 300 350 400 10 20 30 40 50 60 70 80 90 50 100 150 200 250 300 350 400 20 40 60 80 100 120 140 50 100 150 200 250 300 350 400

CaF2(pure) Liquid Scintillator CaF2(pure) +Liquid Scintillator Pulse Height(10mV/ch) Time(10ns/ch) Time(10ns/ch) Time(10ns/ch) Liquid Scintillator CaF2(pure) Typical Pulse Shape of Each Scintillators by 100MHz FADC

SLIDE 5

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

0.2 0.4 0.6 0.8 1 500 1000 1500 2000 2500 3000 3500 4000 4500

CaF2 Energy(keV) Ratio Partial/Full

Active Shielding Technique

Concept of 4 Concept of 4π π Active Shield and Performance Test Active Shield and Performance Test

Dual Gate Technique Clear Discrimination

Clear Discrimination between CaF2 and Liquid Scintillators . . .Well Act as Veto Counter

CaF2(pure) Event Full ADC Gate Partial ADC Gate 80nsec 4µsec γ-ray Liquid Scintillator Event β-ray CaF2(pure)

Liq. Scintillator

Energy 2400～2600keV

CaF2(pure) Liquid Scintillator

20 40 60 80 100 0.2 0.4 0.6 0.8 1

Ratio Partial/Full

0νββ 2νββ Charge of Full ADC Gate Charge of Partial ADC Gate Ratio =

SLIDE 6

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Expected Background in CANDLES

2 2νββ νββ Decay Event Decay Event

Improve Energy Resolution

Natural Natural Radioactivities Radioactivities in CaF in CaF2

2(pure) Crystal

(pure) Crystal

Improve Purity of CaF2 Rejection by Offline Analyses

External Background External Background Strongly Suppressed Strongly Suppressed

Because of High Because of High Q Qββ

ββ of

f 48

48Ca(4.27MeV)

Ca(4.27MeV) 4 4π π Active Shielding System Active Shielding System

Remaining Background . . .The Only Decays Remaining Background . . .The Only Decays

10

2

10

1

1 10 10 2 2000 2500 3000 3500 4000 4500 5000

212Bi

experimental Data

0νββ Window 2νββ

208Tl 214Bi

Counts(/20keV) Energy(keV)

Background Studies with CaF2(Eu) System (ELEGANT VI)

212Bi, 214Bi and 208Tl ;

Natural Natural Radioactivities Radioactivities in CaF in CaF2

2(Eu) Crystal

(Eu) Crystal Simulation Serious Background

SLIDE 7

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Energy Resolution: 9.1%(FWHM) at 662keV =3.4% (FWHM) at 4.27MeV(Qββ of 48Ca)

Req. for CANDLES III ; 4.0%

Light Propagation in CANDLES

Energy Resolution with Prototype Detector Energy Resolution with Prototype Detector (CANDLES I) (CANDLES I)

CaF2(pure) (280nm Peak Emission) Liquid Scintillator ; Wave Length Shifter PMT ; 5inch × 4 modules PTFE Reflector Light Collection : ~80% Standard γ Source

250 500 750 1000 1250 1500 200 400 600 800 1000 500 1000 1500 2000 2500 3000 250 500 750 1000 1250 1500 1750

9.14%(FWHM)

137Cs (662keV)

Energy (keV) Counts Energy (keV)

60Co (1.17MeV,1.33MeV)

5.91%(FWHM)

CaF2 Crystal (10cm Cube) Liquid Scintillator (Wave Length Shifter) PMT (Borosilicate Glass) (Borosilicate Glass)

SLIDE 8

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Backgrounds from Natural Radioactivities in Crystals

238U 214Bi 214Po

T1/2 = 164µsec

232Th 212Bi 212Po

T1/2 = 0.299µsec

64% U-Chain Qα = 8.95MeV

Qβ = 3.27MeV Qβ = 2.25MeV

36% Qα = 6.09MeV

210Pb

Qα = 7.83MeV Qβ = 4.99MeV

208Pb

stable

208Tl Event

Sequential Pulse

Development of High Purity CaF2(pure) Crystal Sequential Pulse Rejection by FADC Pulse Shape Discrimination between α and γ rays Space-Time Correlation Cut . . . For 208Tl Rejection For Rejection . . . For Rejection . . .

212Bi 208Pb

stable

232Th

β β β α α α

Th-Chain Th-Chain Emax=5.8MeV(U) 5.3MeV(Th) Emax=5.0MeV

β+α

Sequential Pulse

208Tl

T1/2 = 3.05min 212Bi and 208Tl(T1/2=3min) . . .

Space-Time Correlation Cut

Because . . . CaF2(pure) Decay Constant : 900ns

SLIDE 9

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Development of High Purity CaF2(pure) Crystals

Selection of CaF Selection of CaF2

2 Powder

Powder

Radioactivities in CaF2(pure) Crystal (α-ray measurement by delayed coincidence) Radioactivities in CaF2 Powder (HPGe measurement)

CaF2 Powder Fused CaF2 Raw Materials CaCO3, HF CaF2 Crystal

Growing Process of CaF2(pure) Crystals HPGe Measurement . . . For Measurement in CaF2 Powder

Pb OFHC Cu Ge Detector Pb

Preamp

Sample PL

For Measurement

f CaF2 Powder

: HPGe Detector Sensitivity:～3mBq/kg 170ccGe Schematic Drawing

SLIDE 10

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Delayed Coincidence Measurement

Delayed Coincidence Measurement . . . Radioactivities in Crystals

238U 214Bi 214Po

T1/2 = 164µsec

232Th 220Rn 216Po

T1/2 = 145msec

U-Chain Qα = 8.95MeV

Qβ = 3.27MeV Qβ = 2.25MeV

210Pb

Qα = 7.83MeV

β α α

Th-Chain

212Pb

α Delayed Coincidence = Measurement of 2 Correlated Event in the Chains Prompt Decay + Delayed Decay CaF2 Crystal For Measurement of CaF2 Crystal : Delayed Coincidence Measurement . . . Sensitivity:～5µBq/kg CaF2 Crystal with Reflector Experimental Setup 31µBq/kg

0.5 1 1.5 2 2.5 3 500 1000 1500 2000 2500 3000 3500 4000 ENERGY(keV) COUNTS(/50keV/kg/day)

216Po 220Rn

Typical Energy Spectra(Th-Chain)

SLIDE 11

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Development of High Purity CaF2(pure) Crystals

U-chain(214Bi) : 41µBq/kg (Averaged 42) . . . 1/25 of Previous Crystals Th-chain(220Rn) : 21µBq/kg (Averaged 42) . . . 1/5 of Previous Crystals

in Progress . . .

Check of Radioactivities in many kinds of Powder and Crystals Selection of Powder

Relation between Radioactivities in Powder and Crystal

So far . . .CaF2(Eu) in ELEGANT VI System U-chain(214Bi) :1100µBq/kg Th-chain(220Rn) :98µBq/kg Powder Radioactivity (U-chain) Crystal Radioactivity (U-chain) Powder Radioactivity (Th-chain) Crystal Radioactivity (Th-chain)

10

4

10

3

10

2

10

1

1 1 2 3 4

Crystal ID A B C

Radioactivities (Arbitrary Unit)

Relation between Powder and Crystal High Purity Powder High Purity Crystal High Purity Contaminated

SLIDE 12

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Background Rejection Efficiency by 100MHz FADC

∆T > 30ns(3ch) If Fast Sampling FADC . . . ∆T > 5ns ; Rejection Effi. = 99%

20 40 60 80 100 120

10
5

5 10 15 20

Time(10nsec) Pules Height(CH/10mV/MeV)

20 40 60 80 100 120 50 100 150 200 250 300 350 400

Time(10nsec) Pules Height(CH/10mV/MeV)

20 40 60 80 100 50 100 150 200 250 300 350 400

Time(10nsec) Pules Height(CH/10mV/MeV)

Sequential Pulse

Rejection of Sequential Pulse

Prompt Delayed

232Th

T1/2 = 1.1 x 1010year

212Bi

Qβ=2.2MeV

212Po

Qα=7.8MeV 64%

Prompt Delayed Typical Pulse Shape(100MHz FADC)

Th-Chain Decay Constant of CaF2(pure) ： 0.9µsec

900ns 50ns

Sequential Pulse Sequential Pulse

T1/2 = 0.299µsec β α

SLIDE 13

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Pulse Shape Discrimination

between α and γ rays

1 10 10 2

50

50 100 150 200 250 300 350 400 450

TIME (10 nsec) Pulse Height(CH/10mV/MeV)

1 10 10 2

50

50 100 150 200 250 300 350 400 450

TIME (10 nsec) Pulse Height(CH/10mV/MeV)

Reference Pulse α ray γ ray

Fast Component CaF2 Pulse = 2 Exponential Components

Measurement Best Fit

Fast Slow 111±6ns 894±15ns 38.4±0.2 37.3±0.7 Fast Slow 128±13ns 936±13ns 17.3±0.1 38.1±0.7 Decay Constants Intensity Intensity of Fast Component α ray > γ ray . . .Apply to PSD

SLIDE 14

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Pulse Shape Discrimination

PSD (Event by Event Analysis) PSD (Event by Event Analysis)

FADC (100MHz) Fit with Two Exponential Function (fixed time constants) Ratio ; Afast/Aslow (Intensity of Fast and Slow Component)

between α and γ rays Clear Discrimination between α and γ(β) Events Background Rejection Efficiency > 99.7%

Fast Slow PSD between γ and α rays As Af γ-ray Event α-ray Event Af/As = 0.5(γ-ray) Af/As = 1.0(α-ray)

SLIDE 15

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

CaF2(pure)

Liquid Scintillator

15”PMT Water

Position Correlated Background Rejection

208 208Tl Events

Tl Events

Rejection of 208Tl Events

208Tl Event

232Th

T1/2 = 1.1 x 1010year

212Bi

36%

Prompt α-ray Delayed β-ray

Th-Chain

208Tl

T1/2 = 3.05min

Qβ = 4.99MeV

Reconstruction

f Event Position

Experimental Result For 208Tl Event Rejection . . . Space-Time Correlation Cut The Same Crystal (α and β-rays), T1/2=3min

Check for Space Correlation Cut (Position Reconstruction) Check for Space Correlation Cut (Position Reconstruction)

Pos. Parameter 1

Position Reconstruction

Pos. Parameter 2
0.8
0.6
0.4
0.2

0.2 0.4 0.6 0.8

0.8 -0.6 -0.4 -0.2

0.2 0.4 0.6 0.8

Experimental Setup (CANDLES II) 45cm 15inch PMT

Crystal Position

Liquid Scintillator 45×45×75mm CaF2 ×９ Upper View β α (Pulse Height Ratio 1) (Pulse Height Ratio 2)

SLIDE 16

Saori Umehara, 20th Sep. 2005, US-Japan Seminar

Background Rate

f CANDLES Series

CANDLES Series CANDLES Series

Crystal Total Mass Energy Resolution

214Bi(µBq/kg) in Crystal 212Bi(µBq/kg) in Crystal

2νββ

214Bi 212Bi 208Tl

Expected BG Measuring Time <mν>

CANDLES III

3.2kg×60 crystals 191kg 4.0%(Req.) 50 20 0.01 0.01 0.07 0.04 0.14/year 5 years

0.56 eV CANDLES IV

6.4 ton 3.5%(Req.) 10 1 0.10 0.03 0.10 0.06 0.29/year 6

0.10 CANDLES V

100 ton 3.2%(Req.) 1 0.1 1.33 0.05 0.15 0.10 1.63/year 7

0.03

SLIDE 17

Saori Umehara, 20th Sep. 2005, US-Japan Seminar