talk - International Workshop on Double Beta Decay and Neutrino

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
R&D
= CaF 2 (pure) scintillators + Liquid scintillator system
CANDLES III system at Kamioka underground lab.
Summary
Pre-measurement for performance test
Mass Spectrum of Calcium
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
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
Neutrino-less
double beta decay
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

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

Obtained Result
Energy Spectra(Jan2003-)
Result of ELEGANT VI
COUNTS(/40keV)
10 2
10
1
10 -1
212
Bi
(Sim)
208
Tl
(Sim)
Q of 48 Ca
Run summary (Measurement for 4 years)
Date Number of Expected BG Live Time
Event ( 212 Bi, 214 Bi, 208 Tl) kg・day
Jun1998- 0 1.30 1553
Jan2003- 0 0.27 3394
10 -2
3000 3250 3500 3750 4000 4250 4500 4750 5000
Energy(keV)
No events in 0 Energy Window
0 Half-Life of 48 Ca : > 5.8 × 10 22 year (90% C.L.)

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

Active Shielding Technique
Concept of 4 Active Shield
and Performance Test
PSD between CaF 2
and Liquid Scintillators
Setup
Acrylic Case
:20×20×20cm 3
5inch PMT
Liquid
Scintillator
Liq. Scintillator
γ-ray
CaF 2 (pure)
β-ray
80nsec
4μsec
Partial ADC Gate
Full ADC Gate
Liquid Scintillator
Event
CaF 2 (pure) Event
Ratio Partial/Full
Distribution of “charge ratio”
1
0.8
0.6
0.4
0.2
0
20
Liquid
Scintillator
Clear Discrimination
CaF 2 (pure)
CaF 2 (pure)
:10×10×10cm 3
Energy 2400~2600keV
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
3m diameter × 4m height
Kamioka Lab. Map
(water tank)
KamLAND
Lab D
4m
3m
Super Kamiokande
CANDLES
CANDLES III

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

Pulse Height
800
700
600
500
400
300
200
100
FADC for CANDLES
For CaF 2 and LS signals . . . And data suppression
0
High sampling rate at the beginning, Low sampling at the ending
Typical pulse shape of CaF 2 +LS
500MHz at beginning
~16MHz at end
0 250 500 750 100012501500 17502000
0 1000 2000 3000 4000
Time (nsec)
Pulse Height
800
700
600
500
400
300
200
100
500MHz at beginning
0
-200 -100 0 100 200 300 400
~16MHz at end
-400 0 400 800
Time (nsec)
LS pulse CaF 2 pulse
500MHz×256 16MHz×128
(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
Selective trigger for CaF 2
by using “threshold for integrated signal”
in poster session by M. Saka
Ratio Partial/Full
1
0.8
0.6
0.4
0.2
0
with normal trigger
CaF 2
LS
500 1000 1500 2000 2500 3000 3500 4000 4500
CaF 2
Energy(keV)
at 2600keV
No LS Events
Threshold
for integrated signal
well works.
Pulse Height
800
700
600
500
400
300
200
100
0
Pulse Height
0 250 500 750 1000 1250 1500 1750 2000
Time(2nsec)
800
700
600
500
400
300
200
100
0
CaF 2 Event
CaF 2 + LS
Ratio
0 250 500 750 1000 1250 1500 1750 2000
Time(2nsec)
1
0.8
0.6
0.4
Event Distribution with Trigger for CaF 2
LS Region
CaF 2 +LS
0.2
20
CaF 2
0
0 500 10001500200025003000350040004500 0 Energy(keV)
We obtained . . .
・High efficiency for CaF 2 Scintillator, Low efficiency for LS
80
60
40
at 2600keV

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

For performance test
Pre-measurement
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
238
U
214
Bi
Q = 3.27MeV
214
Po
T 1/2 =164sec
Q = 7.83MeV
206
Pb
stable
- decay
UMEHARA Saori, 16 th Nov. 2011, DBD11

Counts
10 2
Half-life:175±10μsec(164μsec)
energy resolution :=4.3%
radioactivity:61±9(syst.)mBq/kg
(previous measurement:65mBq/kg)
Delayed analysis
214
Bi→ 214 Po→ 210 Pb decay(β→α decay in U-chain)
∆t distribution
0 200 400 600 800 1000
Time(microsec)
Expected performances
with current CANDLES III were obtained.
Counts
Counts
Energy Spectra(∆t

Expected Background
Background Event in CANDLES System
Radioactive Contamination within CaF 2 (pure)
Background process
Th-Chain
232
Th
212
Bi
212
Po
64%
Q = 2.25MeV
T 1/2 = 0.3sec
Pile-up event
(Sequential event)
because . . .
CaF 2 (pure) :
time constant ~1s
208
Pb
stable
Q = 8.95MeV
E max = 5.3MeV
(Q = 4.27MeV)
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
Th-Chain
232
Th
T 1/2 = 1.1 x 10 10 year
Pile-up
212
Bi
Q =2.2MeV
prompt
T 1/2 = 0.3sec
212
Po
64% Q=7.8MeV
delayed
Typical pulse shape of sequential events
Pulse Height
600
500
400
300
Prompt β
200
100
Delayed
Pulse Height
500
400
300
200
100
Decay Constant of CaF 2 (pure)
:0.9sec
with small t
Pulse Height
500
400
300
200
100
0
-100 -50 0 50 100 150 200
Time(2nsec)
0
0 250 500 750 1000 1250 1500 1750 2000
Time(2nsec)
0
0 250 500 750 1000 1250 1500 1750 2000
Time(2nsec)
Sum-up signal of 62 PMT
We can identify the sequential events.
Rejection efficiency > 90%

Pulse Shape Discrimination
Particle Identification between and rays
-ray
-ray
: 214 Po 7.6MeV(E e =2.5MeV)
: 208 Tl 2.6MeV
ref:Shape Indicator
(PRC67(2003) 014310)
Shape Indicator
4
3
2
1
0
-1
-2
-3
-ray events
-ray events
-4
0 500 1000 1500 2000 2500 3000 3500 4000
Energy(keV)
Shape Indicator
Shape Indicator
mean:0(α-ray)
-1.2(γ-ray)
:0.42
・97 % rejection efficiency at 2.6MeV(γ ray:85%)
→95% (+) at 4.27MeV(γ:85%)

R&D : Enrichment of 48 Ca
Enrichment by crown-ether
Crown-ether rings adsorb
Calcium ions
For calcium, 40 Ca adsorption
in crown-ether is slightly prior
Crown-Ether
o
o
40
o
Ca
ion
o o
2、Ca solution
CaCl 2
Natural Ca
fixed flow rate
by pump
1m glass column
Migration length
= 1m
20m
200m
1、Crown-ether resin
packed in column
of 8mm×100cm
40
Ca : captured
Experimental setup
Chromatography:
Breakthrough method
= Migration of Ca solution
in resin area
Enriched 48 Ca
3、Sampling

Result of Enrichment
Isotope Enrichment with Longer Migration Time (Length)
~7hours
1m migration length
larger (volume of Ca)
higher (isotopic ratio)
longer
~70hours
20m
larger
higher
longer
~250hours
200m
Isotope Effect
by Crown-ether
max: 0.0026
Amount of Enrichment by Crown Ether
Isotope Effect (Enrichment Effect)
・The longer migration time(length) =
the larger volume and the higher isotopic ratio
・ 48 Ca enrichment → next CANDLE system
Natural isotopic ratio
= 0.0019

Sensitivity of CANDLES Series
CANDLES series
CANDLES III
Next CANDLES
Crystal
Total Mass
Energy Resolution
2
212
Bi, 208 Tl
Expected BG
3.2kg×96 crystals
305kg
4.0%(Req.)
0.01
0.26
0.27/year
0.5 eV
2 ton
2.8%(Req.)

Summary
ELEGANT VI at Oto Cosmo Obs.
7kg of CaF 2 (Eu) Scintillators
T 1/2 > 5.8 × 10 22 years (< 3.5-22 eV)
CANDLES III at Kamioka Lab.
300kg of CaF 2 (pure) scintillators
Pre-measurement for performance test
Expected sensitivity : 0.5 eV for
R&D (for next CANDLES)
Enriched 48 CaF 2 (pure) scintillators
+ Cooling system for CaF 2 (pure)
Sensitivity : ~0.2 eV~0.05eV
Current status
We started
the measurement
in 2011.
UMEHARA Saori, 16 th Nov. 2011, DBD11