CANDLES for the study of 48 Ca double beta decay T. Kishimoto - - PowerPoint PPT Presentation

SLIDE 1

CANDLES for the study of 48Ca double beta decay

• T. Kishimoto

Osaka Univ.

SLIDE 2

Contents

• Double beta decay and Majorana Mass
• Double beta decay of 48Ca

–ELEGANTS VI

• How to sense 1~10-2 eV region
• CANDLES

–Concept –CANDLES I, II, III, VI, V

• Prospect (Mile Stone)

SLIDE 3

Neutrino has to be Majorana particle

• Dirac mass term
• Majorana mass term

– Left-handed and right- handed particle could have different mass – We have only left handed neutrino. – Heavy right-handed neutrino – Lepton number violation Relativity: Helicity flip mass Double beta decay has to be measured.

SLIDE 4

n p e- νe n p

h h h h V-A V-A

e-

mass term

n p e- νe n p e- νe

2ν mode 0ν mode

2 νβ β sum energy spectrum

48Ca (0+ →

0+) 0 νβ β Energy (MeV) a.u.

0.0 1.0 2.0 3.0 4.0 5.0 0.2 0.4 0.6 0.8 1.0

x 10-5~6

Within Standard model

Double beta decay

SLIDE 5

Current understanding

SLIDE 6

Double beta decay of 48Ca

• Largest Q value (4.27 MeV)

– next largest 150Nd (3.3 MeV) – Large phase space factor – Least background (γ: 2.6 MeV, β: 3.3 MeV)

• Natural abundance → 0.187%

– Enrichment → (no Gas); Hazama – Small amount ~10g

• Next generation

–

M2

if background free –

M4

if background limited

• 76Ge experiment (already seen backgrounds)
• 48Ca (no backgrounds seen) large Q value

∝ ∝

2

/ 1 T Mν ∝ ∝

2

/ 1 T Mν

SLIDE 7

ELEGANT VI

SLIDE 8

ELEGANTS VI

• CaF2(Eu)

– Size 45x45x45 mm3 x 25(23)

• ~6.42 g 48Ca
• passive shield

– OFHC Cu, Pb (γ) – air-tight box + N2 gas purge (Rn) – LiH + paraffin, Cd sheet, H3BO3+H2O tank (n)

• 4π active shield

– CaF2(Eu)+CaF2(pure)

• roll-off ratio (PMT side shield)

– Segmentation (single hit) – CsI(Tl) veto detector

SLIDE 9

Roll-off ratio (4π active shield)

CaF2(pure) as light guide active shield against PMT CaF2(Eu) is not transparent for U.V. light

PMT PMT

CaF2(Eu)

n = 1.44

CaF2(pure)

n = 1.47

Optical grease

n = 1.47

Silicon oil

n = 1.40 CaF2(Eu) CaF2(pure) CaF2(pure)

SLIDE 10

Roll-off ratio

ROLL-O LL-OFF RATIO IO Arbitary Unit RI RIGH GHT(channel) l) LEFT(channel)

R L R L

V V V V R + − =

SLIDE 11

Oto Cosmo Observatory

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

5039.5 m 第一観測室 第二観測室 第三観測室 国道1 6 8 号線 西吉野村側 大塔村側 8 4 5 m

ELEGANT VI

tunnel constructed for railroad (but not used) 470m (1.3 km water equivalent) shield 旧国鉄の五新線（ 奈良県五條市～和歌山県 新宮市） 用の鉄道ト ンネルだが、 結局線路は 敷かれず。

SLIDE 12

Under ground laboratory

SLIDE 13

SLIDE 14

Radioactive Backgrounds

9 2U 9 1P

a

9 0T

h

8 9A

c

8 8R

a

8 7F

r

8 6R

n

8 5A

t

8 4P

• 8

3B

i

8 2P

b 4 . 4 7 x 1 0 y r

U

2 3 8 9

2 4 . 1 0d

T h

2 3 4

6 . 7 5h

P a

2 3 4

2 . 4 5 x 1 0 y r

U

2 3 4 5

8 . x 1 0 y r

T h

2 3 4

1 . 6 x 1 0 y r

R a

2 2 6 3

3 . 8 2d

R n

2 2 2

3 . 5m

P

• 2

1 8

2 6 . 8m

P b

2 1 4

1 9 . 7m

B i

2 1 4

1 6 4 µ s

P

• 2

1 4

2 2 . 3y r

P b

2 1

5 . 1d

B i

2 1

1 3 8 . 4d

P

• 2

1

P b

2 6

S t a b l e 4 . 2 4 . 7 8 4 . 6 9 4 . 7 9 5 . 4 9 6 . 7 . 6 9 5 . 3 1 Qβ= . 1 9 9 Qβ 3 . 2 6 Qβ 1 . 1 6 Qβ . 4 6 Qβ . 6 4

9 2U 9 1P

a

9 0T

h

8 9A

c

8 8R

a

8 7F

r

8 6R

n

8 5A

t

8 4P

• 8

3B

i

8 2P

b

R a

2 2 8

T h

2 3 2

6 . 1 3h

A c

2 2 8

T h

2 2 8

R a

2 2 4

5 5 . 6s

R n

2 2

. 1 5s

P

• 2

1 6

1 . 6 4h

P b

2 1 2

6 . 6m

B i

2 1 2

. 3 0 µ s

P

• 2

1 2

S t a b l e

P b

2 8

4 . 1 5 . 4 2 5 . 6 9 6 . 2 9 6 . 7 8 8 . 7 8 Qβ . 3 9 Qβ 2 . 2 5 Qβ . 5 7 1 . 4 1 x 1 0 y r

1

5 . 7 6y r 1 . 9 1y r 3 . 6 6d Qβ 2 . 1 8 6 . 5 6 4 % 3 6 %

( A ) ( B )

3 . 5 3m

T l

2 8

Qβ 4 . 9 9

8 1T

l

8 0H

g

8 1T

l

8 0H

g

SLIDE 15

Radioactive Contamination

• U-series

– hardware (second) trigger – time window : 9 – 499 µsec.

• Ac-series
• Th-series

– time window : 0.05 – 1.0 (0.5) sec.

sec) 3 . 164 ( Pb Po Bi

210 7687 214 3270 214

µ

α β

   →     → 

= = E E

msec) 781 . 1 ( Pb Po Rn

211 7386 215 6819 219

   →     → 

= =

α α

E E

sec) 145 (0. Pb Po Rn

212 6779 216 6288 220

   →     → 

= =

α α

E E

SLIDE 16

time window : 0.05-1.0 sec

sec) 145 (0. Pb Po Rn

212 6779 216 6288 220

   →     → 

= =

α α

E E

20000 1000 2000

CaF

2-1

50 100 1000 2000

CaF

2 -2

50 100 1000 2000

CaF

2 -3

20 40 1000 2000

CaF

2 -4

50 1000 2000

CaF

2 -5

100 1000 2000

CaF

2-6

50 100 1000 2000

CaF

2 -7

50 1000 2000

CaF

2 -8

50 1000 2000

CaF

2 -9

50 100 1000 2000

CaF

2 -10

25 50 1000 2000

CaF

2 -11

100 1000 2000

CaF

2 -12

25 50 1000 2000

CaF

2 -13

100 1000 2000

CaF

2 -14

100 1000 2000

CaF

2 -15

200 1000 2000

CaF

2 -16

50 1000 2000

CaF

2 -17

100 1000 2000

CaF

2 -18

100 1000 2000

CaF

2 -19

100 1000 2000

CaF

2 -20

20 40 1000 2000

CaF

2 -21

100 1000 2000

CaF

2 -22

50 1000 2000

CaF

2 -23

20 1000 2000

CaF

2 -24

20000 1000 2000

CaF

2 -25

Average contamination Average contamination ( #2 ( #2 － － #24 ) #24 ) U U – – series series 1.11 1.11× ×10 10-

• 3

3 Bq

Bq/kg /kg Ac Ac – – series series 3.84 3.84× ×10 10-

• 4

4 Bq

Bq/kg /kg Th Th – – series series 1.09 1.09× ×10 10-

• 4

4 Bq

Bq/kg /kg U: 1.25x10-5 Bq= 1 ppt Th: 0.1 mBq=24.6 ppt

SLIDE 17

Double Beta Decay of 48Ca Studied by ELEGANT VI

TGV C.L.) (90% years 10 5 . 1 ing Beij C.L.) (76% years 10 5 . 9

21 21 2 / 1

× > × >

ν

T

C.L.) % (90 year 10 4 . 1 C.L.) % (68 year 10 5 . 4

22 22 2 / 1

× > × >

νββ

T

4104 - 4438 keV

C.L.) % (90 eV 7 . 44 ~ 2 . 7 <

ν

m

10-1 1 10 10 2 10 3 2000 3000 4000 5000

Energy (keV) c

• u

n t s / 2 k e V

BG (sim) 2νββ(sim) 0νββ window

Not limited by backgrounds World best value

NPA 730 ’04, 215 0.63 y

SLIDE 18

How to sense mν=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 2νββ decay

• CANDLES is our solution

SLIDE 19

CANDLES

CAlcium fluoride for studies of Neutrino and Dark matrters by Low Energy Spectrometer CaF CaF2

2(Pure)

(Pure) 200kg, 400kg, 6t,100t

48Ca (Qββ=4.27MeV)

Liquid Scintillator Wave Length Shifter 4 π Active Shield Passive shield Photomultiplier Photomultiplier energy resolution

CaF2(Pure)

Liquid Scintillator (Veto Counter)

Buffer Oil Large PMT

SLIDE 20

Big detector

• CaF2 crystal

– Best optical lens – Long attenuation length

• 10m (catalog value for visible light)
• >1m (our measurement for scintillation light)
• Large volume detector

– 10x10x10 cm3 x 600 (6t) (CANDLES IV) – Increase the number of nuclei (48Ca) 6.4 g (ELE VI) ~6(kg) atoms 10 1 . 8

22

×

atoms 10

6 2

～

SLIDE 21

Low Radioactive Background

Active shield (Liquid Scintillator)

• 4π active shield

decay time of the signal

• ～1 µsec

CaF2

• ～10 nsec

liquid scintillator

• passive shield
• Large volume with Low radio activity
• U/Th ～0.1ppt, K ～1ppt
• purification system (U,Th,K,Rn,…)

KamLAND, BOREXINO

SLIDE 22

CANDLES I

POP (Proof of Principle) Detector CaF2(pure) crystal in liquid scintillator (with w.l. shifter) viewed by 4 PMTs (5 inch)

• liq. scint. : mineral oil

+ DPO (3 g/l) + Bis-MSB (0.3 g/l)

CaF2(pure) liquid Scintillator PMT(5")×4

SLIDE 23

Signal discrimination

Liquid Scintillator CaF2

~1 liquid scintillator ~0.04 CaF2

ADC(fast)/ADC(total)

SLIDE 24

Signal discrimination

ADC(fast)/ADC(total) ADC(total)

Signal from Liquid scintillator CaF2

57Co source

Co source

SLIDE 25

Low background material

• Backgrounds @ ~4 MeV

– Maximum energy

• γ~ 2.6 MeV, β~3.3 MeV, α(max)~2.5 MeV(quench)

– Successive decay of α β γ

• ~1µsec decay time

10

• 2

10

• 1

1 10 10 2 2000 2500 3000 3500 4000 4500 5000

212Bi

experimental Data

0νββ Window 2νββ

208Tl 214Bi

Counts(/20keV) Energy(keV)

Emax=5.8MeV(U) 5.3MeV(Th)

β+α

Pulse shape

Gate width(4µsec )

SLIDE 26

Backgrounds

U-Chain

214Po T1/2 = 164µsec

212Bi

212Po

T1/2 = 0.299µsec

64%

Qα = 8.95MeV

Qβ = 2.25MeV

36%

Qα = 6.09MeV Qα = 7.83MeV Qβ = 4.99MeV

212Bi

β β β α α α

208Tl

T1/2 = 3.05min

214Bi 210Pb 238U

Qβ = 3.27MeV

Th-Chain

208Pb

stable

232Th

High Purity CaF2(pure) Crystal Rejection of double pulse Pulse Shape Discrimination between α and γ rays Space-Time Correlation Cut . . . For 208Tl Rejection Rejection . . . Rejection . . .

Th-Chain

208Pb

stable

232Th

SLIDE 27

Rejection of Double Pulse

212Bi

64%

Qβ = 2.25MeV

β Reduction 100MHz FADC

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

20 40 60 80 100 120

• 10
• 5

5 10 15 20

Time(10nsec) Pules Height(CH/10mV/MeV)

20 40 60 80 100 120 50 100 150 200 250 300 350 400

Time(10nsec) Pules Height(CH/10mV/MeV)

20 40 60 80 100 50 100 150 200 250 300 350 400

Time(10nsec) Pules Height(CH/10mV/MeV)

Prompt Delayed

Typical Pulse Shape(100MHz FADC)

900ns 50ns Qα = 7.83MeV

Qβ = 3.27MeV

212Po

T1/2 = 0.299µsec

α

Qα = 8.95MeV

SLIDE 28

Pulse Shape Discrimination

• PSD (Event by Event)

PSD (Event by Event)

– FADC (100MHz) – Afast/Aslow (Fast and slow component)

Fast Slow PSD between γ and α rays As Af γ-ray Event α-ray Event Af/As = 0.5(γ-ray) Af/As = 1.0(α-ray)

Difference in decay time between α and γ rays

Discrimination between α and γ(β) Events Background Reduction ~ 0.3%

SLIDE 29

Development of Low Background CaF2 Crystals

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

Where do is the crystals contaminated? Radioactivities in CaF2(pure) Crystal (α-ray measurement)

Fused CaF2 CaF2 Crystal

Radioactivities in CaF2 Powder (HPGe measurement)

CaF2 Powder Raw Materials CaCO3, HF

Powder selection Crystal making

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

SLIDE 30

High resolution CaF2 crystal

• Resolution
• Scintillation light

– ~1/2 of CaF2(Eu) (quart window PMT) – peak emission U.V. (285 nm)

• Increase # of photons

– Wavelength shifter – UV visible light

p

N E 1 ~ ∆

SLIDE 31

Wavelength shifter

CaF2 UV light Maximum light output @ 0.3g/l PPO Pseudocumene reduces it.

→Two phase

SLIDE 32

Two Phase System

CaF2(Pure)

Concept of Method

• Conversion Phase

– Large conversion eff. – good transparency for UV

• Veto Phase

– Large light output with aromatic solvent

CaF2 Emission (~285nm) Conversion by WLS(350~400nm) PMT propagate

SLIDE 33

Side View

250 500 750 1000 1250 1500 200 400 600 800 1000

9.14%(FWHM) Energy (keV) Counts

500 1000 1500 2000 2500 3000 250 500 750 1000 1250 1500 1750

Energy (keV)

60Co (1333keV)

5.91%(FWHM)

137Cs

(662keV)

CaF2(pure)

Liquid Scintillator Standard γ Source

CANDLES I with 10 cm3 CaF2(pure)

(WLS phase)

Energy Resolution: 9.1%(FWHM) at 662keV =3.4% (FWHM) at 4.27MeV

• Req. for CANDLES III ; 4.0%

Performance

SLIDE 34

CANDLES-II

45cm H2O 15”PMT Mount System CaF2(Pure)

10cm cube

Liquid Scintillator

50 100 150 200 250 300

• 1 -0.75 -0.5 -0.25

0.25 0.5 0.75 1

• 1
• 0.75
• 0.5
• 0.25

0.25 0.5 0.75 1

• 1 -0.75 -0.5 -0.25

0.25 0.5 0.75 1

Cosmic-ray Events (High Energy)

Index 1.44@586nm (CaF2) Index 1.46@586nm (Mineral Oil)

• Prototype

S.Umehara

SLIDE 35

CANDLES III

• Construction almost completed @ Osaka Univ.
• CaF2(pure)

– 103 cm3 × 60 crystal; 191 kg – ~400 kg @ underground lab.

• Liquid scintillator

–

φ1000×h1000 acrylic container

• Purification system (Ogawa)
• H2O Buffer

passive shield

–

φ2800×h2600

– safety regulation

• PMTs

– 15” PMT (×8) : R2018 – 13” PMT (×32) : R8055

SLIDE 36

CANDLES III

Handrail Water Tank for CANDLES III 280cm 260cm

PMT 280cm φ 100cm φ 260cm

Water Buffer

100cm

WLS Phase CaF2(pure) Veto Phase

CaF2 Module Liquid Scintillator

Outside View Outside View

CaF2(pure) : 10×10×10cm3 60 Crystals (191kg)

SLIDE 37

CANDLES III

Inside View Inside View

Photomultiplier Tube(13inch)

Tank for Liquid Scintillator (Acrylic Case)

40 PMTs Version And 60 PMTs Version . . . Funded

SLIDE 38

CANDLES IV

CaF2(Pure)

Liquid Scintillator (Veto Counter)

Buffer Oil Large PMT

1.BG 1.Needs R&D 2.Energy resolution 1.Buy PMT & gain adjust 15×15×15 cm3 CaF2 (600 cubes) 6.4 t liquid scintillator Vessel ( 48Ca) 6.4 kg

SLIDE 39

CANDLES and world projects

CANDLES III IV V

48Ca

Beijin ELEGANT VI Majorana GENIUS

76Ge

HDM IGEX MOON

100Mo

NEMO3 ELEGANT V CAMEO

116Cd

CUORECINO CUORE COBRA

130Te

EXO XMASS

136Xe 150Nd

0.01 0.1 1 10

1

Milano

mν (eV)

Caltech UCI Kiev

SLIDE 40

Mile stone

• ELEGANTS VI

– running with new BG rejection (2ν)

• CANDLES I, II, POP
• CANDLES III (under construction @ our lab.)

– CaF2(10cm3) 200kg:sea level, 400 kg; UG lab. – ~30 µBq/kg for ~0.5 eV

• CANDLES IV

– 15cm3 cube (600 crystals) 6.4t; Kamioka – ~3 µBq/kg for ~0.1 eV in 6 years

• CANDLES V

– 100t; SNO or Kamland or … for ~30meV in 7years achieved

SLIDE 41

Sensitivity of CANDLES Series

Now 2006 2007 2008

CANDLES IV CANDLES III

3.2kg×60 crystals 191kg 4.0%(Req.) 50 20 0.01 0.01 0.07 0.04 0.14/year 5 years

0.56 eV CANDLES IV

6.4 ton 3.5%(Req.) 10 1 0.10 0.03 0.10 0.06 0.29/year 6

0.10 CANDLES V

100 ton 3.2%(Req.) 1 0.1 1.33 0.05 0.15 0.10 1.63/year 7

0.03

Crystal Total Mass Energy Resolution

214Bi(µBq/kg) 212Bi(µBq/kg)

2νββ

214Bi 212Bi 208Tl

Expected BG Measuring Time <mν>

Performance @ sea Level Lab. CANDLES III Measurement @ Underground Lab. Construction start

SLIDE 42

Prospects

• If the detector to sense 0.03 eV is ever built,

– Majorana neutrino – Neutrino mass

• Next generation detector

– Much bigger

• CANDLEC IV (6.4t)

– Further bigger

• CANDLES V (100t)
• SNO, Kamland
• Further option: Enrichment