talk - International Workshop on Double Beta Decay and Neutrino
talk - International Workshop on Double Beta Decay and Neutrino
talk - International Workshop on Double Beta Decay and Neutrino
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CANDLES for the study<br />
for <strong>Double</strong> <strong>Beta</strong> <strong>Decay</strong> of 48 Ca<br />
UMEHARA Saori<br />
umehara@rcnp.osaka-u.ac.jp<br />
CANDLES collaborati<strong>on</strong><br />
Osaka University, University of Fukui, University of Tokushima,<br />
Hiroshima University, Saga University,<br />
Kyoto San-gyo University<br />
48<br />
Ca Enrichment<br />
Tokyo Institute of Technology,<br />
Sophia University
Outline<br />
<strong>Double</strong> beta decay of 48 Ca<br />
ELEGANT VI system (previous system)<br />
= CaF 2 (Eu) scintillators + CsI(Tl) scintillators system<br />
CANDLES System<br />
R&D<br />
= CaF 2 (pure) scintillators + Liquid scintillator system<br />
CANDLES III system at Kamioka underground lab.<br />
Summary<br />
Pre-measurement for performance test<br />
Mass Spectrum of Calcium<br />
40<br />
Ca<br />
42<br />
Ca<br />
43<br />
Ca<br />
44<br />
Ca<br />
46<br />
Ca<br />
48<br />
Ca<br />
×10 ×0.1 ×0.1 ×0.1 ×0.001 ×0.1<br />
UMEHARA Saori, 16 th Nov. 2011, DBD11
<strong>Double</strong> <strong>Beta</strong> <strong>Decay</strong><br />
<strong>Double</strong> <strong>Beta</strong> <strong>Decay</strong><br />
<strong>Neutrino</strong>-less double beta decay<br />
Very rare decay T 1/2 > (~10 25 years)<br />
nucleus<br />
If observed<br />
<strong>Neutrino</strong> → Majorana particle<br />
Lept<strong>on</strong> number violati<strong>on</strong><br />
<strong>Decay</strong> rate T 1/2 ∝ 1/m<br />
2<br />
<br />
We have studied double beta decay of 48 Ca<br />
<strong>Neutrino</strong>-less<br />
double beta decay<br />
<br />
<br />
<br />
UMEHARA Saori, 16 th Nov. 2011, DBD11
<strong>Double</strong> <strong>Beta</strong> <strong>Decay</strong> of 48 Ca<br />
Why 48 Ca?<br />
Higher Q -value(4.27MeV) . . .<br />
76<br />
Ge(2.0MeV), 100 Mo(3.0MeV), 130 Te(2.5MeV)<br />
→Low background<br />
because Q -value is higher than BG<br />
E max =2.6MeV( 208 Tl, -ray)<br />
3.3MeV( 214 Bi,-ray)<br />
We have developed the detector system<br />
for no background measurement<br />
<strong>Double</strong> beta decay of 48 Ca by CaF 2 scintillators<br />
ELEGANT VI system<br />
Scale up<br />
CANDLES series
Schematic drawing of ELEGANT VI<br />
CaF 2 (Eu)<br />
CaF 2 (pure)<br />
CsI(Tl)<br />
ELEGANT VI<br />
ELEGANT VI<br />
ELEctr<strong>on</strong> Gamma-ray <strong>Neutrino</strong> Telescope<br />
CaF 2 Scintillator (CaF 2 (Eu))<br />
23 Crystals(45×45×45cm 3 :290g)<br />
Source of <strong>Decay</strong> : 48 Ca<br />
(Q =4.27MeV)<br />
veto counters<br />
46 CaF 2 (pure)<br />
38 CsI(Tl)<br />
→ 4 Active Shield<br />
Air-tight Box<br />
LiH<br />
Cu<br />
Pb<br />
Passive shields<br />
for -ray<br />
Cu : 5cm,Pb : 10cm<br />
for Neutr<strong>on</strong><br />
LiH+Paraffin :15mm<br />
Cd sheet : 0.6mm<br />
H 3 BO 3 loaded water<br />
UMEHARA Saori, 16 th Nov. 2011, DBD11
Obtained Result<br />
Energy Spectra(Jan2003-)<br />
Result of ELEGANT VI<br />
COUNTS(/40keV)<br />
10 2<br />
10<br />
1<br />
10 -1<br />
212<br />
Bi<br />
(Sim)<br />
208<br />
Tl<br />
(Sim)<br />
Q of 48 Ca<br />
Run summary (Measurement for 4 years)<br />
Date Number of Expected BG Live Time<br />
Event ( 212 Bi, 214 Bi, 208 Tl) kg・day<br />
Jun1998- 0 1.30 1553<br />
Jan2003- 0 0.27 3394<br />
10 -2<br />
3000 3250 3500 3750 4000 4250 4500 4750 5000<br />
Energy(keV)<br />
No events in 0 Energy Window<br />
0 Half-Life of 48 Ca : > 5.8 × 10 22 year (90% C.L.)<br />
Design C<strong>on</strong>cepts of CANDLES<br />
CANDLES<br />
CAlcium fluoride for studies of <strong>Neutrino</strong> <strong>and</strong> Dark matrters<br />
by Low Energy Spectrometer<br />
Liquid Scintillator<br />
(Veto Counter)<br />
CaF 2 (pure) scintillator<br />
L<strong>on</strong>g attenuati<strong>on</strong> length (>10m@350nm)<br />
<strong>Double</strong> beta decay source<br />
48<br />
Ca (Q bb =4.27MeV)<br />
Liquid scintillator<br />
4 Active Shield<br />
Large photomultiplier tube<br />
Signals from both scintillators<br />
are detected simultaneously<br />
CaF 2 (pure)<br />
Buffer Oil<br />
Active Shielding Technique<br />
Different time c<strong>on</strong>stants<br />
CaF 2 (pure) : ~1sec<br />
Liquid scintillator : a few 10 nsec<br />
Large PMT<br />
UMEHARA Saori, 16 th Nov. 2011, DBD11
Active Shielding Technique<br />
C<strong>on</strong>cept of 4 Active Shield<br />
<strong>and</strong> Performance Test<br />
PSD between CaF 2<br />
<strong>and</strong> Liquid Scintillators<br />
Setup<br />
Acrylic Case<br />
:20×20×20cm 3<br />
5inch PMT<br />
Liquid<br />
Scintillator<br />
Liq. Scintillator<br />
γ-ray<br />
CaF 2 (pure)<br />
β-ray<br />
80nsec<br />
4μsec<br />
Partial ADC Gate<br />
Full ADC Gate<br />
Liquid Scintillator<br />
Event<br />
CaF 2 (pure) Event<br />
Ratio Partial/Full<br />
Distributi<strong>on</strong> of “charge ratio”<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
20<br />
Liquid<br />
Scintillator<br />
Clear Discriminati<strong>on</strong><br />
CaF 2 (pure)<br />
CaF 2 (pure)<br />
:10×10×10cm 3<br />
Energy 2400~2600keV<br />
500 1000 1500 2000 2500 3000 3500 4000 4500<br />
CaF 2<br />
Energy(keV)<br />
Clear Discriminati<strong>on</strong> between CaF 2 <strong>and</strong> Liquid Scintillators<br />
. . .Well Act as Veto Counter<br />
UMEHARA Saori, 16 th Nov. 2011, DBD11
CANDLES III at Kamioka Lab.<br />
CANDLES at Kamioka underground Lab.<br />
CANDLES III<br />
3m diameter × 4m height<br />
Kamioka Lab. Map<br />
(water tank)<br />
KamLAND<br />
Lab D<br />
4m<br />
3m<br />
Super Kamiok<strong>and</strong>e<br />
CANDLES<br />
CANDLES III
CANDLES III<br />
Main detector<br />
CaF 2 Scintillators<br />
(305kg)<br />
Liquid Scintillator<br />
Tank(2m 3 )<br />
CANDLES III<br />
CANDLES at Kamioka underground laboratory<br />
CaF 2 scintillator (CaF 2 (pure))<br />
305 kg (96 modules × 3.2kg)<br />
~ 1sec<br />
Liquid scintillator (LS)<br />
4 Active Shield<br />
Volume:2m 3<br />
~ a few ten nsec<br />
Large photomultiplier tube<br />
13inch PMT × 48<br />
20inch PMT × 14<br />
13inch <strong>and</strong> 20inch<br />
PMTs<br />
for CANDLES III system<br />
・Characteristic FADC<br />
for CaF 2 (l<strong>on</strong>g)<br />
<strong>and</strong> LS(short) signals<br />
・Selective trigger for CaF 2
Pulse Height<br />
800<br />
700<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
FADC for CANDLES<br />
For CaF 2 <strong>and</strong> LS signals . . . And data suppressi<strong>on</strong><br />
0<br />
High sampling rate at the beginning, Low sampling at the ending<br />
Typical pulse shape of CaF 2 +LS<br />
500MHz at beginning<br />
~16MHz at end<br />
0 250 500 750 100012501500 17502000<br />
0 1000 2000 3000 4000<br />
Time (nsec)<br />
Pulse Height<br />
800<br />
700<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
500MHz at beginning<br />
0<br />
-200 -100 0 100 200 300 400<br />
~16MHz at end<br />
-400 0 400 800<br />
Time (nsec)<br />
LS pulse CaF 2 pulse<br />
500MHz×256 16MHz×128<br />
(Sum at FPGA)<br />
Clear Discriminati<strong>on</strong> between CaF 2 <strong>and</strong> Liquid scintillators<br />
・Details of PSD will be presented in a poster sessi<strong>on</strong> by G. Ito<br />
Data size is small.<br />
・500MHz×2048data → 500MHz×256data + 16MHz×128data<br />
~
Selective Trigger<br />
Selective trigger for CaF 2<br />
by using “threshold for integrated signal”<br />
in poster sessi<strong>on</strong> by M. Saka<br />
Ratio Partial/Full<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0<br />
with normal trigger<br />
CaF 2<br />
LS<br />
500 1000 1500 2000 2500 3000 3500 4000 4500<br />
CaF 2<br />
Energy(keV)<br />
at 2600keV<br />
No LS Events<br />
Threshold<br />
for integrated signal<br />
well works.<br />
Pulse Height<br />
800<br />
700<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
0<br />
Pulse Height<br />
0 250 500 750 1000 1250 1500 1750 2000<br />
Time(2nsec)<br />
800<br />
700<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
0<br />
CaF 2 Event<br />
CaF 2 + LS<br />
Ratio<br />
0 250 500 750 1000 1250 1500 1750 2000<br />
Time(2nsec)<br />
1<br />
0.8<br />
0.6<br />
0.4<br />
Event Distributi<strong>on</strong> with Trigger for CaF 2<br />
LS Regi<strong>on</strong><br />
CaF 2 +LS<br />
0.2<br />
20<br />
CaF 2<br />
0<br />
0 500 10001500200025003000350040004500 0 Energy(keV)<br />
We obtained . . .<br />
・High efficiency for CaF 2 Scintillator, Low efficiency for LS<br />
80<br />
60<br />
40<br />
at 2600keV
Positi<strong>on</strong> Rec<strong>on</strong>structi<strong>on</strong><br />
250<br />
200<br />
150<br />
100<br />
50<br />
Positi<strong>on</strong> Rec<strong>on</strong>structi<strong>on</strong><br />
for events with CaF 2 pulse shapes<br />
for identificati<strong>on</strong> of CaF 2 positi<strong>on</strong><br />
Counts<br />
positi<strong>on</strong>(X)<br />
5CaF 2 s<br />
0<br />
-500-400-300-200-100 0 100 200 300 400 500<br />
Positi<strong>on</strong> X<br />
Counts<br />
Counts<br />
We can identify each CaF 2 positi<strong>on</strong>.<br />
in a poster sessi<strong>on</strong> by K. Yasuda<br />
225<br />
200<br />
175<br />
150<br />
125<br />
100<br />
75<br />
50<br />
25<br />
0<br />
-500-400-300-200-100 0 100 200 300 400 500<br />
Positi<strong>on</strong> Y<br />
300<br />
250<br />
200<br />
150<br />
100<br />
50<br />
positi<strong>on</strong>(Y)<br />
positi<strong>on</strong>(Z)<br />
Lower<br />
3 CaF 2 s<br />
6 layers<br />
Upper<br />
0<br />
-500-400-300-200-100 0 100 200 300 400 500<br />
Positi<strong>on</strong> Z
For performance test<br />
Pre-measurement<br />
by st<strong>and</strong>ard source<br />
in a poster presentati<strong>on</strong> by H. Kakubata<br />
by radioactive c<strong>on</strong>taminati<strong>on</strong>s within a reference CaF 2<br />
Delayed analyses<br />
214<br />
Bi→ 214 Po(U-chain)<br />
219<br />
Rn→ 215 Po(Ac-chain)<br />
220<br />
Rn→ 216 Po(Th-chain)<br />
U-chain<br />
238<br />
U<br />
214<br />
Bi<br />
Q = 3.27MeV<br />
<br />
214<br />
Po<br />
T 1/2 =164sec<br />
Q = 7.83MeV<br />
<br />
206<br />
Pb<br />
stable<br />
- decay<br />
UMEHARA Saori, 16 th Nov. 2011, DBD11
Counts<br />
10 2<br />
Half-life:175±10μsec(164μsec)<br />
energy resoluti<strong>on</strong> :=4.3%<br />
radioactivity:61±9(syst.)mBq/kg<br />
(previous measurement:65mBq/kg)<br />
Delayed analysis<br />
214<br />
Bi→ 214 Po→ 210 Pb decay(β→α decay in U-chain)<br />
∆t distributi<strong>on</strong><br />
0 200 400 600 800 1000<br />
Time(microsec)<br />
Expected performances<br />
with current CANDLES III were obtained.<br />
Counts<br />
Counts<br />
Energy Spectra(∆t
Expected Background<br />
Background Event in CANDLES System<br />
Radioactive C<strong>on</strong>taminati<strong>on</strong> within CaF 2 (pure)<br />
Background process<br />
Th-Chain<br />
<br />
232<br />
Th<br />
212<br />
Bi<br />
212<br />
Po<br />
64%<br />
Q = 2.25MeV<br />
T 1/2 = 0.3sec<br />
Pile-up event<br />
(Sequential event)<br />
because . . .<br />
CaF 2 (pure) :<br />
time c<strong>on</strong>stant ~1s<br />
<br />
208<br />
Pb<br />
stable<br />
Q = 8.95MeV<br />
E max = 5.3MeV<br />
(Q = 4.27MeV)<br />
To reject as the sequential event (background event)<br />
・identify the “pile-up” shape<br />
・ rays particle identificati<strong>on</strong><br />
UMEHARA Saori, 16 th Nov. 2011, DBD11
Sequential Events<br />
212<br />
Bi→ 212 Po decay<br />
Th-Chain<br />
232<br />
Th<br />
T 1/2 = 1.1 x 10 10 year<br />
Pile-up<br />
212<br />
Bi<br />
Q =2.2MeV<br />
prompt<br />
T 1/2 = 0.3sec<br />
212<br />
Po<br />
64% Q=7.8MeV<br />
delayed<br />
Typical pulse shape of sequential events<br />
Pulse Height<br />
600<br />
500<br />
400<br />
300<br />
Prompt β<br />
200<br />
100<br />
Delayed <br />
Pulse Height<br />
500<br />
400<br />
300<br />
200<br />
100<br />
<br />
<strong>Decay</strong> C<strong>on</strong>stant of CaF 2 (pure)<br />
:0.9sec<br />
with small t<br />
Pulse Height<br />
500<br />
400<br />
300<br />
200<br />
100<br />
0<br />
-100 -50 0 50 100 150 200<br />
Time(2nsec)<br />
0<br />
0 250 500 750 1000 1250 1500 1750 2000<br />
Time(2nsec)<br />
0<br />
0 250 500 750 1000 1250 1500 1750 2000<br />
Time(2nsec)<br />
Sum-up signal of 62 PMT<br />
We can identify the sequential events.<br />
Rejecti<strong>on</strong> efficiency > 90%
Pulse Shape Discriminati<strong>on</strong><br />
Particle Identificati<strong>on</strong> between <strong>and</strong> rays<br />
-ray<br />
-ray<br />
: 214 Po 7.6MeV(E e =2.5MeV)<br />
: 208 Tl 2.6MeV<br />
ref:Shape Indicator<br />
(PRC67(2003) 014310)<br />
Shape Indicator<br />
4<br />
3<br />
2<br />
1<br />
0<br />
-1<br />
-2<br />
-3<br />
-ray events<br />
-ray events<br />
-4<br />
0 500 1000 1500 2000 2500 3000 3500 4000<br />
Energy(keV)<br />
Shape Indicator<br />
Shape Indicator<br />
mean:0(α-ray)<br />
-1.2(γ-ray)<br />
:0.42<br />
・97 % rejecti<strong>on</strong> efficiency at 2.6MeV(γ ray:85%)<br />
→95% (+) at 4.27MeV(γ:85%)
R&D : Enrichment of 48 Ca<br />
Enrichment by crown-ether<br />
Crown-ether rings adsorb<br />
Calcium i<strong>on</strong>s<br />
For calcium, 40 Ca adsorpti<strong>on</strong><br />
in crown-ether is slightly prior<br />
Crown-Ether<br />
o<br />
o<br />
40<br />
o<br />
Ca<br />
i<strong>on</strong><br />
o o<br />
2、Ca soluti<strong>on</strong><br />
CaCl 2<br />
Natural Ca<br />
fixed flow rate<br />
by pump<br />
1m glass column<br />
Migrati<strong>on</strong> length<br />
= 1m<br />
20m<br />
200m<br />
1、Crown-ether resin<br />
packed in column<br />
of 8mm×100cm<br />
40<br />
Ca : captured<br />
Experimental setup<br />
Chromatography:<br />
Breakthrough method<br />
= Migrati<strong>on</strong> of Ca soluti<strong>on</strong><br />
in resin area<br />
Enriched 48 Ca<br />
3、Sampling
Result of Enrichment<br />
Isotope Enrichment with L<strong>on</strong>ger Migrati<strong>on</strong> Time (Length)<br />
~7hours<br />
1m migrati<strong>on</strong> length<br />
larger (volume of Ca)<br />
higher (isotopic ratio)<br />
l<strong>on</strong>ger<br />
~70hours<br />
20m<br />
larger<br />
higher<br />
l<strong>on</strong>ger<br />
~250hours<br />
200m<br />
Isotope Effect<br />
by Crown-ether<br />
max: 0.0026<br />
Amount of Enrichment by Crown Ether<br />
Isotope Effect (Enrichment Effect)<br />
・The l<strong>on</strong>ger migrati<strong>on</strong> time(length) =<br />
the larger volume <strong>and</strong> the higher isotopic ratio<br />
・ 48 Ca enrichment → next CANDLE system<br />
Natural isotopic ratio<br />
= 0.0019
Sensitivity of CANDLES Series<br />
CANDLES series<br />
CANDLES III<br />
Next CANDLES<br />
Crystal<br />
Total Mass<br />
Energy Resoluti<strong>on</strong><br />
2<br />
212<br />
Bi, 208 Tl<br />
Expected BG<br />
<br />
3.2kg×96 crystals<br />
305kg<br />
4.0%(Req.)<br />
0.01<br />
0.26<br />
0.27/year<br />
0.5 eV<br />
2 t<strong>on</strong><br />
2.8%(Req.)<br />
Summary<br />
ELEGANT VI at Oto Cosmo Obs.<br />
7kg of CaF 2 (Eu) Scintillators<br />
T 1/2 > 5.8 × 10 22 years (< 3.5-22 eV)<br />
CANDLES III at Kamioka Lab.<br />
300kg of CaF 2 (pure) scintillators<br />
Pre-measurement for performance test<br />
Expected sensitivity : 0.5 eV for <br />
R&D (for next CANDLES)<br />
Enriched 48 CaF 2 (pure) scintillators<br />
+ Cooling system for CaF 2 (pure)<br />
Sensitivity : ~0.2 eV~0.05eV<br />
Current status<br />
We started<br />
the measurement<br />
in 2011.<br />
UMEHARA Saori, 16 th Nov. 2011, DBD11