1

Study of 48Ca Double Beta Decay by CANDLES

T. KishimotoOsaka Univ.

2

Why 48Ca• Highest Q value (4.27 MeV)

– next largest 150Nd (3.3 MeV)– Large phase space factor – Little BG （ natural radioactivity : 2.6 MeV, : 3.3 MeV ）

• Natural abundance: 0.187%– Huge amount of CaF2 crystals– Isotope separation: expensive (no Gas) 　– Early studies (recent studies use separated isotope)

• Next generation – M ~ T-1/2 ~ M-2 (no BG)

~ M-4 （ BG limited ）C.L.) % (90 eV 7.44~2.7m

NPA 730 　’ 04, 215

48Ca (no BG)

Double Beta Decay of 48Ca Studied by ELEGANT VI

4104 - 4438 keV

0.63 y

48Ca double beta decay

10 -1

1

10

10 2

10 3

2000 3000 4000 5000Energy (keV)

coun

ts/2

0ke

V

no events in 0 window

(Q0=4.27 MeV)

T1/2 > 1.8× 1022 yr (90%C.L.)

BG (sim)

2(sim)

0 window

C.L.) % (90year 104.1 2202/1 T

C.L.) % (90 eV 7.44~2.7m

NPA 730 　’ 04, 215

Not limited by backgrounds

1.76 y

Yet no BG

C.L.) % (90 eV 7.21~5.3m

But only 6.4g of 48Ca

4

CANDLES

CaFCaF22(Pure)(Pure) 200kg, 300kg, 3t,30t(2%) 48Ca (200g, 300g, 3kg, 300kg)

Liquid ScintillatorWave Length Shifter4 Active ShieldPassive shield

PhotomultiplierPhotomultiplier energy resolution

CaF2(Pure)

Liquid Scintillator(Veto Counter)

Buffer Oil

Large PMT

CAlcium fluoride for studies of Neutrino and Dark matrtersby Low Energy Spectrometer

21COE Sep 11, Osaka

5

CANDLES IRejection of ext. BG

Liquid Scintillator

CaF2

ADC(fast)ADC(total) CaF2(pure)

liquid ScintillatorPMT(5")× 4

ADC(total)

Liquid Scintillator

CaF2

CANDELS IPOP detector

Background @ Q value region• No natural BG @ ~4 MeV

– Maximum energy• ~ 2.6 MeV, ~3.3 MeV, ~2.5 MeV(quench~0.3)

– Successive decay of • ~1sec decay time

100MHz FADC 　　 T > 30ns(3ch) ; ~5% 500MHz FADC (under preparation) T > 5ns ; ~1%

212Bi ()

212Po ()

Pulse shape

7

Pulse Shape Discrimination

• PSD (Event by Event)PSD (Event by Event)– FADC (100MHz)– Afast/Aslow (Fast and slow component)

Difference in decay time between and rays

Discrimination between and Events　　 Background Reduction ~ 0.3%

8

Development of Low Radioactive CaF2

• delayed coincidence• @ Oto Cosmo observatory

0

5

10

15

20

25

30

35

40

45

50

0 - 0.01

- 0.02

- 0.03

- 0.04

- 0.05

- 0.06

- 0.07

- 0.08

- 0.09

- 0.10

- 0.12

- 0.14

- 0.16

- 0.18

- 0.20

(mBq/kg)不純物濃度

個数 U系列

Th系列

U~36Bq/kg14 (best)

Th~20Bq/kg6 (best)N

umbe

r of C

aF2 c

ryst

als

mBq/kg

95 crystals

3t 600k 300k

9

Energy resolution and BG rejection (2 phase)

CaF2(Pure)

• CaF2: UV region (PMT)• Conversion layer

– UV→visible (PMT)– UV transparent

• Veto layer– Liq scint ： absorb UV

CaF2 Emission (~285nm)

Conversion by WLS(350~400nm)

PMT

propagate

9.14%(FWHM)

Energy (keV)

Cou

nts

137Cs (662keV)

21COE Sep 11, Osaka

10

CANDLES III (prototype)

10cm3 x 56 CaF200×h2600

11

CANDLES IIIInside ViewInside View Photomultiplier Tube(13inch)

Tank for Liquid Scintillator (Acrylic Case)40 PMTs Version

Buffer water

Test measurement just started @ Osaka (sea level)

2007/03/25 日本物理学会春の大会＠首都大学東京

Crystal with huge BG

1st 2nd

3rd 4th 5th

no crystals

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Mile stone• ELEGANTS VI

– running with new BG rejection (2)• CANDLES I, II• CANDLES III

– 10cm3 cube (100 crystals) ~0.5 eV– BG of CaF2 ~30 Bq/kg (<100 Bq/kg )

• CANDLES III(UG) • CANDLES IV

– 10cm3 cube (1000 crystals) 3.2t– BG of CaF2 ~10 Bq/kg for 0.2 eV – Kamioka

Achieved Kamioka

DUSEL town meetingNov. 2-4, Washington DC

14

CANDLES

XMASS

SK

KamLand

New experimental Hall under excavation

15

Future

• CANDLES V to sense ~10 meV region – ~30 ton CaF2 and 2% enrichment– Further large space

• Kamland, SNO (Vessel and PMT’s)• DUSEL

• Isotope enrichment– Available: 76Ge, 100Mo, 128Te– exception: 48Ca, 150Nd

• R&D in progress– Crown ether (Resin is made)

• Current separation constant is a bit low.