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CANDLES for the study of 48Ca double beta decay

T. Kishimoto

RCNP & Physics Dept.

Osaka Univ.

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Contents

• Double beta decay and Majorana Mass –Matter dominated universe–Neutrino mass– Majorana neutrino and double beta decay

• Double beta decay of 48Ca• CANDLES detector

–Concept–CANDLES I, II, III, VI, V

• Prospect

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Baryon density in our Universe• Big bang nucleosynthesis

– 4He, D, 3He, 7Li– Baryon density

B ~ 10 － 10

If particle number is conserved, Particle ：Anti-particle ：

Matter dominated Univ. →CP + particle # →Double Deta decay

Relativity + uncertainty →anti-particle

present

future

past

・ no information is faster than light・ interact with any space-time→particle that travels backward in time→anti-particleCarries inverse quantity (charge spin(chirality))

Charge: conservedChirality: violated by mass

distance

timelight

Dirac equation→anti-particle

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Neutrino type

• type Dirac Weyl Majorana• components 4 2 2 x 2• 　　　　　　　　　　　　　　　　　　　　　　　　　 L R

particle

Anti-particle

C, PCP

m=0 m≠0

Lepton numberChirality

Direction of propagation

mL mR

oscillationm

~55 meV ~7 meV

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Direct measurement of m

• 3H – decay (Q: 18.7keV)

• 0 decay

• CMBR– WMAP +

SDSS + …

KATRIN　=>　m　~ 0.2　eV

KATRIN　=>　m　~ 0.2　eV

m　<　~　0.6　eVm　<　~　0.6　eV

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02 decay

n p

e -e

n p

hh

h

hV -A

V -A

e -

m a s s te r m

n p

e - e

n p

e - e

2 m o d e

0 m o d e

Possible in Standard model

Majorana particleparticle⇔anti-particle・ possible only for ・ matter dominated universe

.....||

|)00(|2200

102/1

mMG

T

NM

Phase volume

Nuclear matrix element

Effective mass

2　mode

Sum　energy　spectrum

0　modeT　>1025　

yrT　~1019　yr

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has to be a Majorana particle

• Mass term (Dirac)

• Mass term (Majorana)– Only Left (right) handed

mass term can be made– Left and right can have

different mass – We know only left-handed

neutrino – Heavy right-handed

（ see-saw mechanism ）– Violates lepton number

Chirality flip （ relativity ）

Left handed → right handed (anti-particle)

Leptogenesis

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Leptogenesis

• GUT ? (No proton decay?) SK

• Majorana particle （ Lepton number ）– particle anti-particle

• CP– Anti-lepton ＞ Lepton 　 (~10-10)

• Instanton effect (t’Hooft)– Standard model– Anti-lepton → baryon

• conserved ： B-Lpositron 　 　 proton

Fukugita, Yanagida (1986)

Proton decay(B-L cons.) is irrelevant to the Baryogenesis : Yanagida

Effective in early universe

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Double beta decay nuclei

• Nuclei – 48Ca, 76Ge, 82Se,100Mo,– 128Te, 130Te, 136Xe, 150Nd– Positron emitter

• Ultra rare process – 1020~25 yr

• Huge natural background sources – High sensitive detector– Low background circumstance⇔Underground

lab.

AZN

AZ+1N-1

AZ+2N-2

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World Experiments

Cla im by KKK

CANDLES

48Ca 76Ge 100Mo82Se 130Te 136Xe 150Nd

0.01

0.1

1

101

IV

V

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Why 48Ca• Highest Q value (4.27 MeV, 150Nd: 3.3 MeV)

– Large phase space factor – Little BG （ : 2.6 MeV, : 3.3 MeV ）

• Natural abundance → 0.187%– Isotope separation → expensive (no Gas) 　

• ~10g x 2 (in the world. only Early studies)• Next generation

– M ~ T-1/2 ~ M-2 (no BG) ~ M-4 （ BG limited ）

– 48Ca (no BG so far)• If we want to sense normal hierarchy region,

only 48Ca + enrichment has a chance.

Nuclear matrix element

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n1

e

p1

p1

n1

e

n1e

p1

p1

n1

e

q1~0q2~0

q2 + q1~0q2 - q1~pF

ifrrqqiedr ))(( 2121

if

i f

2 decay

0 decay

ifdr

2 nucleon correlationNeutrino potential 1/r~A-1/3

F2N(q=0)

F2N(q)

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p n

f7/2

f5/2

Matrix element 48Ca

forbidden if only f7/2(wf) And GT(op)

wf: Configuration mixingOp: Higher partial wave

A=48

・

|M0|2 ~5 ambiguity (accept and challenge) M(48Ca) is well estimated but not perfect yet. It is small though taken to be the minimum.

M0

M. Horoi (2010)

Oto Cosmo Observatory

5 03 9 .5 m

第 一 観 測 室第 二 観 測 室 第 三 観 測 室

国 道 168号 線

西 吉 野 村 側

大 塔 村 側

845m

A tunnel constructed for a railroad but never used. It is 60km south from Osaka

ELEGANT VI

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

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

NPA 730 　’ 04, 215

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神岡

大 塔 コ ス モ 観 測 所

大阪大学核物理研究センター

大阪大学理学部

48Ca double beta decay by ELEGANT VI

NPA 730 　’ 04, 215

Not limited by backgrounds

1.76 y

But only 6.4g of 48Ca 16

C.L.) % (90 eV 22~5.3mC.L.) % (90year 108.5 220

2/1 T

PRC78 058501(‘08)

Q of 48Ca

PMT PMT

CaF2(Eu)n = 1.44CaF2(pure)

n = 1.47

Optical greasen = 1.47

Silicon oiln = 1.40

CaF2(Eu)

CaF2(pure)

CaF2(pure)

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How to sense m=1~10-2eV• Big detector

– Huge amount of materials

• Low radioactive background– Active shield– Passive shield– Low background material– BG rejection by signal processing

• High resolution– Backgrounds from 2 decay

• CANDLES is our solution

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CANDLES

CaFCaF22(Pure)(Pure)

200kg, 300kg, 3t, enrichment

48Ca (Q=4.27MeV)

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

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CANDLES IBackground rejection

Liquid Scintillator

CaF2

ADC(fast)ADC(total)

CaF2(pure)

liquid ScintillatorPMT(5")× 4

ADC(total)

Liquid Scintillator

CaF2

POP(Proof of Principle)

liq. scint. : mineral oil + DPO 　　　 (3 g/l)+ Bis-MSB (0.3 g/l)

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

Rejection of Double Pulse

Prompt

Delayed

Typical Pulse Shape(100MHz FADC)

900ns 50ns

212Bi212Po

T1/2 = 0.299sec64%Q = 8.95MeV

Q = 3.27MeV

Q = 2.25MeV

Q = 7.83MeV

208Pb

Sum energy ~ Q value

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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%

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Development of Low Background CaF2 Crystals

Radioactivities in CaF2(pure) Crystal(-ray measurement)

Radioactivities in CaF2 Powder(HPGe measurement)

U-chain(214Bi) ~41Bq/kg . . . 1/25 of Previous CrystalsTh-chain(220Rn) ~21Bq/kg . . . 1/5 of Previous Crystals

CaF2 Powder

FusedCaF2

Raw MaterialsCaCO3, HF

CaF2 Crystal

Where is the crystals contaminated?

Powder selection Crystal making

CaF2(Eu) in ELEGANT VI U-chain(214Bi) : 1100Bq/kg Th-chain(220Rn) : 98Bq/kg

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Radioactive impurities

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

U系列

Th系列

3t 600k 300kCANDLES III(U.G.)CANDLES IV

Energy resolution and BG rejection (2 phase system)

CaF2(Pure)

• BG from 2

• Energy resolution

• CaF2 ： UV – PMT

• 2 phase system 9.14%(FWHM)

Energy (keV)

Cou

nts

137Cs (662keV)

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UV

Visible light

Veto phase (absorves UV)

Conversionphase

CaF2(pure)

Liquid ScintillatorCANDLES I (WLS phase)

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H2O

15”PMT

Mount System

CaF2(Pure)10cm cube

Liquid Scintillator

CANDLES-II

• Prototype

45cm

Cosmic-ray Events (High Energy)

Index 1.44@586nm (CaF2)

Index 1.46@586nm (Mineral Oil)

S.Umehara

CANDLES III@Osaka

Tank: Φ2.8×h2.6 m

PMT:13”×3215”× 　 8

CaF2: 　 191 kg103 　 cm3×60

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Rejection ofexternal BG

Observation at sea levelUnderground OK

Kamioka Experimental hall D

CANDLES III(UG)3m ×4m h

CANDLES III （ UG ）

Lab D

Super Kamiokande

KamLAND

CANDLES

Kamioka

4m3m

CANDLES III(UG)

CANDLES III （ UG ）

CANDLES III （ UG ）62 PMT’s

96 CaF2(pure) crystals

(CaF2 crystals)

Almost completed

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Mile stone• ELEGANTS VI

– Best 48Ca 0limit

• CANDLES I, II

• CANDLES III+ III(UG)– 100 x10cm3 CaF2 (~30Bq/kg) ~0.5 eV

– Start running in this October.

• CANDLES IV – 3t CaF2 (3.5 kg 48Ca) (~3Bq/kg) ~0.1 eV

• CANDLES V– Enrichment and 0.3~1t of 48Ca (m≦10meV)

achieved

Characteristic of CANDLES

• BG rate (events/weight)– So far the best

• 2~3 orders

• Scale up: – CANDLES IV, V

• Enrichment – more nuclei– BG reduction

Target Project Abund. (%)

Background rate (counts/kg/year)

48Ca ELEGANT VI 0.187 0 (measured)0.075 (expected)

CANDLES III 0.187 5x10-4

CANDLES IV 0.187 5x10-5

76Ge HDM ~86 0.61

130Te CUORICINO 33.9 2.4

CUORE 33.9 0.8 (CUORE-0)10-2~10-3(Goal)

136Xe EXO-200 ~80 0.1

+ Ba tagging

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Achieve both simultaneously

Enrichment of 48Ca• Increase nuclei

• BG reduction

• Crown ether– Sep. coeff. 　 ε~ (3.5±0.5)x10-3

– Crown ether resin

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O

O O

O

OO

C C

C

C

C

C

C C

Dicyclohexano 18-crown-6

DC18C6Ca2+

- -

- -

- -

48Ca ： 0.2% => 5~10 %

Enrichment for long migrationEnrichment for long migration

~7 hours~7 hours1m1m

~70~70 hourshours20m20m

~250~250 hourshours200m200m

Enrichment due to crown ether

・ long migration length ・ higher enrichment and larger amount ~7 時間 (1m) → ~250 時間　 (200m) amount: ×17, enrichment: ×8

P r e l i m i n a r ymaximum: 0.0026(original:0.0019)

Ca ions in CE

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• Why CE absorbs 40Ca more than 48Ca? – CE: Harmonic oscillator pot.

• Heavier Ca is in a lower energy state.

– Water: （pH: 10-14 mol/ℓ）• H2O: polar molecule: HO pot.

• Partition function ⇔ distribution

– Mass dependence

)2

1( nEn

CE

water

E

14848

48

2

)(31

kTExp

nWCE

WCE

m

k

2.0)12.1( meV~1% effect

Other enrichment methods

• Laser ionization – Plant for Uranium enrichment– KAERI 1kUS$/g (~1/100 of current CM value)

• Centrifuge: high (0.6 MG) (JAERI)• Electrophoresis • Others

• We will clarify the separation method in an year.

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Thank you.