Search for Neutrino-less Double Beta
Decay with CANDLES
UMEHARA Saori
[email protected]
T. Kishimoto, M.Nomachi, S. Ajimura, S.Yoshida, K.Matsuoka, N. Nakatani,
K. Ichimura, G.Ito, K.Yasuda, H.Kakubata, M. Saka, K. Takubo, K. Seki, W. Wang,
Y.Tamagawa, I.Ogawa, K.Fushimi, R.Hazama, H. Ohsumi, K.Okada
CANDLES collaboration
Osaka University, University of Fukui, University of Tokushima,
Hiroshima University, Saga University,
Kyoto San-gyo University
Y. Fujii, Y. Sakuma, M. Nomura, T. Suzuki, T. Kaneshiki, S. Nemoto
Tokyo Institute of Technology,
Sophia University
Outline
Double Beta Decay of 48Ca
ELEGANT VI System (previous system)
= CaF2(Eu) scintillators + CsI(Tl) scintillators system
Result
CANDLES System (next system)
= CaF2(pure) scintillators + Liquid scintillator system
CANDLES III system (at Kamioka Underground Lab.)
Pre-measurement (without liquid scintillator)
Mass Spectrum of Calcium
R&D
48Ca
40Ca
enrichment
42
Summary
×10
Ca
43Ca
44Ca
×0.1
×0.1
×0.1
46Ca
×0.001
48Ca
×0.1
UMEHARA Saori, 28th Jul. 2011, PANIC11
Double Beta Decay
Double Beta Decay
Two neutrino double beta decay
within Standard model
→already observed
Neutrino-less double beta decay
(~1025years)
not obserbed T1/2 >
cf. H.V. Klapdor-Kleingrothaus et al.
If observed
Neutrino → Majorana particle
Lepton number violation
Decay rate T1/2 ∝ 1/m2
Neutrino-less
double beta decay

nucleus


UMEHARA Saori, 28th Jul. 2011, PANIC11
Double Beta Decay
Experimental study for double beta decay
because double beta decay = rare decay
Large amount of double beta nuclei
a few kg ~ a few ton
Low background condition
1/m ∝ T1/2 ∝ Mdetector
if no background
1/m ∝ T1/2 ∝ Mdetector1/2
if background limited
Nuclei and measurement of double beta decay
for example . . .
76Ge
100Mo
130Te
136Xe
48Ca
: Klapdor et al., IGEX, MAJOANA, GERDA
: NEMO3→SuperNEMO, ELE V→MOON
: Cuoricino→CUORE
: EXO, NEXT,
: Our group(ELEGANT VI→CANDLES)
th
UMEHARA Saori, 28 Jul. 2011, PANIC11
Double Beta Decay of 48Ca
Why 48Ca?
Higher Q-value(4.27MeV) . . .
76Ge(2.0MeV),100Mo(3.0MeV),130Te(2.5MeV)
→Low background
because Q-value is higher than BG
Emax=2.6MeV(208Tl, -ray)
3.3MeV(214Bi,-ray)
We have developed the detector system
for no background measurement
Double Beta Decay of 48Ca by CaF2 Scintillators
ELEGANT VI system
Scale up
CANDLES series
UMEHARA Saori, 28th Jul. 2011, PANIC11
ELEGANT VI
ELEGANT VI
ELEctron Gamma-ray Neutrino Telescope
Schematic drawing of ELEGANT VI
CaF2(Eu)
CaF2 Scintillator (CaF2(Eu))
23 Crystals(45×45×45cm3:290g)
Source of Decay : 48Ca
(Q=4.27MeV)
veto counters
46 CaF2(pure)
38 CsI(Tl)
→ 4 Active Shield
CaF2(pure)
CsI(Tl)
LiH
Air-tight Box
Cu
Pb
Passive shields
for -ray
Cu : 5cm,Pb : 10cm
for Neutron
LiH+Paraffin :15mm
Cd sheet : 0.6mm
H3BO3 loaded water
UMEHARA Saori, 28th Jul. 2011, PANIC11
Result of ELEGANT VI
Obtained Result
COUNTS(/40keV)
Energy Spectra(Jan2003-)
Q of 48Ca
10
Run summary (Measurement for 4 years)
2
Date
10
212Bi
(Sim)
1
Number of
Event
Expected BG
(212Bi,214Bi,208Tl)
Live Time
kg・day
Jun1998- 0
1.30
1553
Jan2003- 0
0.27
3394
208Tl
10
10
-1
(Sim)
-2
3000 3250 3500 3750 4000 4250 4500 4750 5000
No events in 0 Energy Window
Energy(keV)
0 Half-Life of 48Ca : > 5.8 × 1022 year (90% C.L.)
<m < (3.5-22) eV
For higher sensitivity, we need a large
amount of 48Ca.
UMEHARA Saori, 28th Jul. 2011, PANIC11
Design Concepts of CANDLES
CANDLES
CAlcium fluoride for studies of Neutrino and Dark matrters
by Low Energy Spectrometer
Undoped CaF2 scintillator (CaF2(Pure))
Liquid Scintillator
(Veto Counter)
Long attenuation length (>10m@350nm)
Double beta decay source
48Ca (Q =4.27MeV)
bb
Liquid scintillator
4  Active Shield
Large photomultiplier tube
Signals from both scintillators
are detected simultaneously
Active Shielding Technique
Different time constants
CaF2(pure)
: ～1sec
Liquid scintillator : a few 10 nsec
CaF2(Pure)
Buffer Oil
Large PMT
UMEHARA Saori, 28th Jul. 2011, PANIC11
Active Shielding Technique
Concept of 4 Active Shield
and Performance Test
PSD between CaF2
and Liquid Scintillators
Setup
Acrylic Case
:20×20×20cm3
5inch PMT
80nsec
Liq. Scintillator
γ-ray
4μsec
Partial ADC Gate
Full ADC Gate
Liquid Scintillator
Event
CaF2(pure)
β-ray
CaF2(pure) Event
Ratio Partial/Full
Liquid
Scintillator
1
2 0
CaF2(pure)
:10×10×10cm3
Energy 2400～2600keV
0.8
0.6
Liquid
Scintillator
0.4
Clear Discrimination
0.2
CaF2(pure)
0
500 1000 1500 2000 2500 3000 3500 4000 4500
CaF2 Energy(keV)
Clear Discrimination between CaF2 and Liquid Scintillators
. . .Well Act as Veto Counter
UMEHARA Saori, 28th Jul. 2011, PANIC11
CANDLES III at Kamioka Lab.
New experimental room at Kamioka underground Lab.
CANDLES III
3m diameter × 4m height
(water tank)
Kamioka Lab. Map
KamLAND
Lab D
Super Kamiokande
4m
3m
CANDLES
CANDLES III
UMEHARA Saori,
28th Jul. 2011, PANIC11
th
UMEHARA Saori, 12 May. 2010, RCNP
CANDLES III at Kamioka Lab.
CANDLES III
62 PMTs
96 CaF2(pure) Scintillators (~300kg)
Inside Modules
(CaF2 Scintillators)
First measurement
: without LS and water
for check of CaF2 pulse shape
(without LS pulse)
Inside View
of Water Tank
UMEHARA Saori, 28th Jul. 2011, PANIC11
Measurement
without LS and Water
Typical Pulse Shape
200
150
100
50
0
Decay Constant 1sec
= CaF2 Signal
Pulse Height
Sum Signal from 62 PMTs
Pulse Height
250
50
40
Signal from each PMT
PMT22
30
20
Photoelectrons
10
0
-10
100 125 150 175 200 225 250 275 300
0
100
200
300
400
Time(2nsec)
Time(nsec)
200
600 800 100012001400160018002000
200 400 1000
1800
2600
3400
FADC for CANDLES system
Time(2nsec)
Time(nsec)
・ Beginning of pulse : 500MHz FADC
・ Late of pulse
: 16MHz FADC
for Data suppression
UMEHARA Saori, 28th Jul. 2011, PANIC11
Measurement
without LS and water
10
3
Pile-up event
Signals from 48PMTs
Event at 4.5 MeV
= expected BG event
400
Pulse Height
Counts
Energy Spectrum
350
10
300
2
250
200
150
10
100
40K
50
0
208Tl
1
0
1000
2000
3000
4000
5000
Energy(keV)
・ 40K、208Tl can be observed.
→Reference pulse for CaF2 signal
200 400 600 800 100012001400160018002000
400
1200 2000 2800
3600
Time(2nsec)
Time(nsec)
In this measurement . . .
・A high contaminated crystal
as reference crystal
(～30mBq/kg)
We can reject by FADC
June 2011 . . .
UMEHARA Saori, 28th Jul. 2011, PANIC11
We started the measurement with LS and water.
R&D:
Enrichment of 48Ca
for Study of 0by CANDLES
It needs a large amount of 48Ca(~10kg)
→1st Step : Large scale detector : CaF2 of 300kg ~ a few ton
→2nd Step :48Ca enrichment （~2％⇔natural abundance 0.187%）
Technologies for 48Ca Enrichment
Gas diffusion
、、、 ×
Gas centrifuge
、、、 ×
Chemical process 、、、 ○
Isotope enrichment by Crown-Ether
Calcium =
No Gaseous Compound
Crown-Ether
o
Crown-ether rings adsorb Calcium ions
o 40
o
Ca
For calcium,40Ca adsorption in crown-ether
ion
o
o
th
is slightly prior
UMEHARA Saori, 28 Jul. 2011, PANIC11
o
Setup for Enrichment Test
Experimental system
Chromatography：
Breakthrough method
= Migration of Ca solution
in resin area
２、Ca solution
CaCl2
+Conc. HCl
５、Measurement of
isotopic ratio
fixed flow rate
by pump
Migration length = 1m
20m
200m
１、Crown-ether resin
packed in column
４、Measurement of
Ca concentration
Fraction collector
1m glass column
of 8mm×100cm
Water pump
Water
UMEHARA Saori, 28th Jul. 2011, PANIC11
３、Sampling
thermo. bath
by fraction collector
Result of Enrichment
Isotope Enrichment with Longer Migration Time (Length)
~7hours
1m migration length longer
~70hours
20m
longer
~250hours
200m
Isotope Effect
by Crown-ether
max: 0.0026
larger
higher
larger (volume of Ca)
higher (isotopic ratio)
Amount of Enrichment by Crown Ether
Isotope Effect (Enrichment Effect)
Natural isotopic ratio
= 0.0019
・The longer migration time(length) =
the larger volume and the higher isotopic ratio
・We continue to study 48Ca enrichment.
th
UMEHARA Saori, 28 Jul. 2011, PANIC11
Current Rough Estimation
for 2%48Ca、200kg Calcium
Migration time
: ~5~ years
for improvement
Kind of crown-ether
Now:Benzo-18-crown-6-ether
Candidate : for example. . .
Dibenzo-18-crown-6-ether → inexpensive (~1/10)
Optimization of migration parameter
Mass Spectrum
Calcium . . )
Solvent : (now) HCl → (Candidate) Organic
solvent of
(methanol.
Good adsorptive rate
40Ca
42Ca
43Ca
44Ca
46Ca
48
Migration speed
: (now)0.3ml/min,1ml/min→3ml/min.
. . Ca
time effective
×10
×0.1
×0.001
×0.1 ×0.1
×0.1
UMEHARA Saori, 28th Jul. 2011, PANIC11
Summary
ELEGANT VI at Oto Cosmo Obs.
7kg of CaF2(Eu) Scintillators
T1/2 > 5.8 × 1022 years (< 3.5-22 eV)
CANDLES III at Kamioka Lab.
300kg of CaF2(pure) scintillators
Expected sensitivity : 0.5 eV for <m>
R&D (for next CANDLES )
Current status
We started
the measurement
in June.
Enriched 48CaF2(pure) scintillators
Sensitivity : ~0.2 eV~0.05eV
UMEHARA Saori, 28th Jul. 2011, PANIC11
UMEHARA Saori, 28th Jul. 2011, PANIC11
Backgrounds
Radioactive Contaminations in CaF2 Crystals
Pile-up
because of
 of CaF2 signal = 1sec
Pile-up Events
Th-Chain
232Th
208Tl
212Bi

212Po
64%
T1/2 = 0.3sec

208Tl

208Pb
+
stable
Emax=5.3MeV(Th-chain)
5.8MeV(U-chain)
Event
Th-Chain
232Th
212Bi
36%
3.0min
Q = 5.0MeV
T1/2 =


208Pb
stable
Emax=5.0MeV
212Bi
and 208Tl(T1/2=3min) . . .
Space-Time Correlation Cut
2 Events
Possible to reduce by good energy resolution
. . . negligible in CANDLES III (expected resolution = ~4% at 4.27MeV)
Background Rejection
Pile-up Events . . . Pulse Shape Analysis by using FADC
UMEHARA Saori, 28th Jul. 2011, PANIC11
Rejection of Pile-up Events
Pile-up Events
Pile-up
Th-Chain
212Bi
232Th

T1/2 = 0.3sec
212Po

Q=2.2MeV 64% Q=7.8MeV
T1/2 = 1.1 x 1010year
Shape Indicator
Pulse Height (ch)
Prompt
Delayed
Typical pulse shape(500MHz FADC)
Particle discrimination between  and -rays
160
140
120
100
t=
890ns
80
easily identified
60
20
10
5
0
40
0
ray
-5
20
00
100
1000
200
2000
300
3000
400
4000
500
5000
Time(nsec)
:2MeV
-ray
15
-10
0
500
1000
1500
2000
:600keV
2500
3000
Energy(keV)
Pile-up event rejection ~99%
Clear discrimination for t > 5nsec
Rejection by particle discrimination
99%28th Jul. 2011, PANIC11
UMEHARA~Saori,
→Improvement with 4 order of magnitude
Setup for Long Migration
Setup for Long Migration Experiment (200m migration)
for high enriched Ca
Regeneration & Reuse of Resin (by removing Ca ion)
Original
Ca Solution
- Experimental Setup -
1m × 200 columns
1m
In this experiment,
18 times 12 columns = ~200m
Enriched 48Ca
Study for possibility of high enrichmentth
UMEHARA Saori, 28 Jul. 2011, PANIC11
by long migration length
Rejection of LS Signals
Rejection by using FADC Data
3 Types of Pulse Shapes
 of CaF2 = 900nsec
LS = ~20nsec
CaF２
150
100
50
0
250
200
150
TimeTime(2ns)
(nsec)
250
200
100
50
50
0
0
100 -100
150 200
250 200
300 300
350 400
400 500
450 600
500
-200
0 100
TimeTime(2ns)
(nsec)
100 -100
150 200
250 200
300 300
350 400
400 500
450 600
500
-200
0 100
TimeTime(2ns)
(nsec)
Charge in partial gate = large
Charge in partial gate = small
Charge-Ratio =
LS
150
100
partial gate
full gate
100 -100
150 200
250 300
400 500
450 600
500
-200
0 100
200 350
300 400
CaF2+LS
Pulse Height
200
Pulse Height
Pulse Height
Typical Pulse Shapes
250
charge in partial gate
charge in full gate
We can clearly discriminate between CaF2 and others
UMEHARA Saori, 28th Jul. 2011, PANIC11