CANDLES for the study for Double Beta Decay of 48 Ca UMEHARA Saori - - PowerPoint PPT Presentation

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CANDLES for the study for Double Beta Decay of 48 Ca UMEHARA Saori - - PowerPoint PPT Presentation

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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

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SLIDE 1

CANDLES for the study for Double Beta Decay of 48Ca

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

48Ca Enrichment

Tokyo Institute of Technology, Sophia University

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SLIDE 2

×10 ×0.1 ×0.1 ×0.1 ×0.1 ×0.001

40Ca 42Ca 43Ca 44Ca 46Ca 48Ca

Mass Spectrum of Calcium

Outline

Double beta decay of 48Ca ELEGANT VI system (previous system)

= CaF2(Eu) scintillators + CsI(Tl) scintillators system

CANDLES System

= CaF2(pure) scintillators + Liquid scintillator system

CANDLES III system at Kamioka underground lab.

Pre-measurement for performance test

R&D Summary

UMEHARA Saori, 16th Nov. 2011, DBD11

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SLIDE 3

Double Beta Decay

Double Beta Decay

Neutrino-less double beta decay

Very rare decay T1/2 > (~1025years) If observed Neutrino → Majorana particle Lepton number violation Decay rate T1/2 ∝ 1/m

2

We have studied double beta decay of 48Ca

  nucleus 

Neutrino-less double beta decay

UMEHARA Saori, 16th Nov. 2011, DBD11

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SLIDE 4

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

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SLIDE 5

ELEGANT VI

ELEGANT VI ELEctron Gamma-ray Neutrino Telescope

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 Passive shields for -ray Cu : 5cm,Pb : 10cm for Neutron LiH+Paraffin :15mm Cd sheet : 0.6mm H3BO3 loaded water CsI(Tl) CaF2(pure) CaF2(Eu) Cu Pb LiH Air-tight Box Schematic drawing of ELEGANT VI

UMEHARA Saori, 16th Nov. 2011, DBD11

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SLIDE 6

Result of ELEGANT VI

Obtained Result No events in 0 Energy Window

10

  • 2

10

  • 1

1 10 10 2 3000 3250 3500 3750 4000 4250 4500 4750 5000

Energy(keV) COUNTS(/40keV)

212Bi

(Sim)

208Tl

(Sim)

Q of 48Ca

0 Half-Life of 48Ca : > 5.8 × 1022 year (90% C.L.) <m < (3.5-22) eV ・4 active shield is effective for background free measurement. ・Expected backgrounds are 212Bi and 208Tl

Date Number of Event Expected BG (212Bi,214Bi,208Tl) Live Time kg・day Jun1998-

1.30 1553

Jan2003-

0.27 3394 Run summary (Measurement for 4 years) Energy Spectra(Jan2003-)

For higher sensitivity, we need a large amount of 48Ca.

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SLIDE 7

Design Concepts of CANDLES

CaF2(pure) scintillator

Long attenuation length (>10m@350nm) Double beta decay source

48Ca (Qbb=4.27MeV)

Liquid scintillator

4  Active Shield Large photomultiplier tube Signals from both scintillators are detected simultaneously CANDLES CAlcium fluoride for studies of Neutrino and Dark matrters by Low Energy Spectrometer

CaF2(pure)

Liquid Scintillator (Veto Counter)

Buffer Oil Large PMT

Active Shielding Technique Different time constants CaF2(pure) : ～1sec Liquid scintillator : a few 10 nsec

UMEHARA Saori, 16th Nov. 2011, DBD11

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SLIDE 8

Acrylic Case :20×20×20cm3

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 Active Shield and Performance Test

PSD between CaF2 and Liquid Scintillators

Setup

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

5inch PMT Liquid Scintillator CaF2(pure) :10×10×10cm3

Energy 2400～2600keV

CaF2(pure) Liquid Scintillator

0 2

UMEHARA Saori, 16th Nov. 2011, DBD11

Distribution of “charge ratio”

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SLIDE 9

CANDLES III at Kamioka Lab.

Lab D Super Kamiokande KamLAND CANDLES

CANDLES at Kamioka underground Lab.

CANDLES III

3m diameter × 4m height (water tank) Kamioka Lab. Map

4m 3m

CANDLES III

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SLIDE 10

CANDLES III

CaF2 scintillator (CaF2(pure)) 305 kg (96 modules × 3.2kg)  ~ 1sec Liquid scintillator (LS) 4  Active Shield Volume:2m3

 ~ a few ten nsec

Large photomultiplier tube 13inch PMT × 48 20inch PMT × 14

CANDLES at Kamioka underground laboratory

for CANDLES III system ・Characteristic FADC for CaF2 (long) and LS(short) signals ・Selective trigger for CaF2

CANDLES III

Main detector CaF2 Scintillators (305kg) 13inch and 20inch PMTs Liquid Scintillator Tank(2m3)

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SLIDE 11

100 200 300 400 500 600 700 800

  • 200
  • 100

100 200 300 400

  • 400 0 400 800

Time (nsec) Pulse Height

100 200 300 400 500 600 700 800 250 500 750 10001250150017502000

1000 2000 3000 4000

Time (nsec) Pulse Height

FADC for CANDLES

For CaF2 and LS signals . . . And data suppression

High sampling rate at the beginning, Low sampling at the ending

Typical pulse shape of CaF2+LS Clear Discrimination between CaF2 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 CaF2 pulse LS pulse 500MHz at beginning ~16MHz at end 500MHz at beginning ~16MHz at end 500MHz×256 16MHz×128 (Sum at FPGA) ～

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SLIDE 12

0.2 0.4 0.6 0.8 1 500 10001500200025003000350040004500 0 20 40 60 80 Energy(keV) Ratio

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

CaF2 Energy(keV) Ratio Partial/Full

Selective Trigger

CaF2 Event Event Distribution with Trigger for CaF2

with normal trigger

No LS Events Threshold for integrated signal well works. LS Region CaF2+LS CaF2 We obtained . . . ・High efficiency for CaF2 Scintillator, Low efficiency for LS LS CaF2

Selective trigger for CaF2

by using “threshold for integrated signal”

in poster session by M. Saka CaF2 + LS

at 2600keV at 2600keV

100 200 300 400 500 600 700 800 250 500 750 1000 1250 1500 1750 2000 Time(2nsec) Pulse Height 100 200 300 400 500 600 700 800 250 500 750 1000 1250 1500 1750 2000 Time(2nsec) Pulse Height

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SLIDE 13

50 100 150 200 250

  • 500-400-300-200-100 0

100 200 300 400 500 Position X

50 100 150 200 250 300

  • 500-400-300-200-100 0

100 200 300 400 500 Position Z 25 50 75 100 125 150 175 200 225

  • 500-400-300-200-100 0

100 200 300 400 500 Position Y

Position Reconstruction

Position Reconstruction

for events with CaF2 pulse shapes for identification of CaF2 position

We can identify each CaF2 position. in a poster session by K. Yasuda

Counts Counts Counts

position(X)

position(Z) position(Y) 5 CaF2s 3 CaF2s Upper Lower 6 layers

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SLIDE 14

Pre-measurement

For performance test

by standard  source in a poster presentation by H. Kakubata by radioactive contaminations within a reference CaF2

Delayed  analyses

214Bi→214Po（U-chain） 219Rn→215Po（Ac-chain） 220Rn→216Po（Th-chain)

UMEHARA Saori, 16th Nov. 2011, DBD11

238U 214Bi 214Po

T1/2 =164sec

Q = 7.83MeV

Q = 3.27MeV

206Pb

stable

 

U-chain

- decay

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SLIDE 15

Delayed  analysis

energy resolution ：=4.3% Half-life：175±10μsec（164μsec）

214Bi→214Po→210Pb decay（β→α decay in U-chain）

10 2 200 400 600 800 1000 Time(microsec) Counts

20 40 60 80 100 120 140 160 180 200 500 1000 1500 2000 2500 3000 3500 4000 Energy(keV) Counts

∆t distribution Energy Spectra(∆t <300sec)

214Bi Q

prompt events

experimental data simulation

25 50 75 100 125 150 175 200 500 1000 1500 2000 2500 3000 3500 4000 Energy(keV) Counts

214Po

delayed events

experimental data fitting

radioactivity：61±9(syst.)mBq/kg （previous measurement:65mBq/kg） Expected performances with current CANDLES III were obtained.

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SLIDE 16

Expected Background

Background Event in CANDLES System

Radioactive Contamination within CaF2(pure)

232Th 212Bi

212Po

64% Q = 8.95MeV

Q = 2.25MeV

208Pb

stable

Th-Chain

 T1/2 = 0.3sec 

Pile-up event (Sequential event)

Emax = 5.3MeV (Q = 4.27MeV)  because . . . CaF2(pure) : time constant ~1s

Background process To reject as the sequential event (background event) ・identify the “pile-up” shape ・  rays particle identification

UMEHARA Saori, 16th Nov. 2011, DBD11

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SLIDE 17

100 200 300 400 500 250 500 750 1000 1250 1500 1750 2000 Time(2nsec) Pulse Height

Sequential Events

Pile-up

232Th

T1/2 = 1.1 x 1010year

212Bi

Q=2.2MeV

212Po

Q=7.8MeV 64%

prompt delayed

Th-Chain

T1/2 = 0.3sec  

212Bi→212Po decay

100 200 300 400 500

  • 100
  • 50

50 100 150 200 Time(2nsec) Pulse Height

100 200 300 400 500 600 250 500 750 1000 1250 1500 1750 2000 Time(2nsec) Pulse Height

Typical pulse shape of sequential events

Delayed  Prompt β Sum-up signal of 62 PMT

with small  t We can identify the sequential events. Rejection efficiency > 90%

Decay Constant of CaF2(pure) ：0.9sec

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SLIDE 18

Pulse Shape Discrimination

  • 4
  • 3
  • 2
  • 1

1 2 3 4 500 1000 1500 2000 2500 3000 3500 4000 Energy(keV) Shape Indicator

・97 % rejection efficiency at 2.6MeV（γ ray:85%） →95% (+) at 4.27MeV（γ:85%）

Particle Identification between  and  rays

mean：0（α-ray）

  • 1.2（γ-ray）

 ：0.42

Shape Indicator Shape Indicator

-ray ：214Po 7.6MeV(Ee=2.5MeV) -ray ：208Tl 2.6MeV

ref：Shape Indicator (PRC67(2003) 014310) -ray events -ray events

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SLIDE 19

R&D : Enrichment of 48Ca

Experimental setup

fixed flow rate by pump

２、Ca solution CaCl2 １、Crown-ether resin packed in column

  • f 8mm×100cm

３、Sampling 1m glass column

= Migration of Ca solution in resin area Chromatography： Breakthrough method

Migration length = 1m 20m 200m Enriched 48Ca Natural Ca

Enrichment by crown-ether

Crown-ether rings adsorb Calcium ions For calcium,40Ca adsorption in crown-ether is slightly prior

  • Crown-Ether

40Ca

ion

40Ca : captured

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SLIDE 20

Result of Enrichment

Isotope Enrichment with Longer Migration Time (Length)

~7hours 1m migration length ~70hours 20m ~250hours 200m Amount of Enrichment by Crown Ether

longer longer

・The longer migration time(length) = the larger volume and the higher isotopic ratio ・48Ca enrichment → next CANDLE system

Isotope Effect (Enrichment Effect)

larger (volume of Ca) higher (isotopic ratio) larger higher

Isotope Effect by Crown-ether max: 0.0026 Natural isotopic ratio = 0.0019

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SLIDE 21

Sensitivity of CANDLES Series

CANDLES series

CANDLES III 3.2kg×96 crystals 305kg 4.0%(Req.) 0.01 0.26 0.27/year 0.5 eV Next CANDLES 2 ton 2.8%(Req.) <0.2 ~0.1 <0.3 /year 0.05 Crystal Total Mass Energy Resolution 2

212Bi,208Tl

Expected BG <m>

Schedule

CANDLES III

Now 2012 2013 2014 2015

Measurement at Kamioka Lab. sensitivity 0.5eV next CANDLES

48Ca enrichment

Cooling system for CaF2 . . . not funded yet 2% 48Ca and cooling system for CaF2 in a poster presentation by K. Takubo

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SLIDE 22

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 Pre-measurement for performance test Expected sensitivity : 0.5 eV for <m>

R&D (for next CANDLES)

Enriched 48CaF2(pure) scintillators + Cooling system for CaF2(pure) Sensitivity : ~0.2 eV~0.05eV

Current status We started the measurement in 2011.

UMEHARA Saori, 16th Nov. 2011, DBD11