The 0-neutrino double beta decay search

with Tin-loaded liquid scintillator

연세대 : 황명진 , 권영준

서울대 : 곽정원 , 김상열 , 김선기 , 김승천 , 명성숙 ,방형찬 ,

양혜영 , 이주희 , 이직 , 이현수 , 이명재 , 최정훈

세종대 : 김영덕 , 이정일

경북대 : 김홍주 , 소중호 , 양성철

이화여대 : 박일흥 , 한인식

메릴린드대 : 서은숙 , 이무현

IHEP:J.Li

칭화대 :J.J.Zhu,D.He,Q.Yue

Why decay is important?

0-DBD Present best experimental limits

1.8

<m>* (eV)

6.0> 1.8 102248CaOgawa I. et al., submitted 2002

Belli et al. submitted PLB

Experiment

< 1.4 4.1> 7 1023136Xe

Range <m>T1/20(y)Isotope

1.01.94.8

0.380.35

Bernatowicz et al. 1993

Zdenko et al. 2002

Ejiri et al. 2001

Aalseth et al 2002

Klapdor-Kleingrothaus et al. 2001

1.5Mi DBD 2002 < 0.9 2.1> 2.1 1023130Te< 1.0 4.4> 7.7 1024128Te< 1.8 6.2> 1.3 1023116Cd< 1.4 - 256> 5.5 1022100Mo< 0.3 - 2.5> 1.57 1025

< 0.3 - 2.5> 1.9 102576Ge

* Staudt, Muto, Klapdor-Kleingrothaus Europh. Lett 13 (1990) 31

Why metal loaded liquid scintillator?

• Advantage a) high-Z can be loaded to LS (>50% or more) b) Fast timing response (few ns) c) Low cost of LS, Large volume is possible d) U/Th/K background for LS is low and purification is known

• Disadvantage a) Bigger volume is necessary (C,H in LS, low

density) b) Lower light output (~15% of NaI(Tl))

Passive shielding at Y2L(700m depth)

Pb shield (15cm)

PE shield (5cm)

Mineral Oil shield (30cm)

Double beta decay detector

Dimension

R = 5cm

H = 14.94cm

V = 1.15L

Plastic

Quartz glass

Teflon

TMSN40%

• TMSN : 347ml (456g, 1.314g/ml)

• PC : 753ml (671g, 0.891g/ml)

• TMSN40% = TMSN + PC

• TMSN : 456g/(456g + 671g) = 40%

• Sn = 456g/(456g + 671g) * 119/178 -> 27%

TMSN40% Calibration

keV keV

-> Resolution 8% , 0.9keV/ADC Channel

• Resolution = 1 / sqrt(N)

Resolution 8% -> 156.25 pe

• 54Mn 834keV

156.25pe/834keV = 0.187pe/keV

TMSN40% Energy Spectrum

by 500MHz FADC

pol3 + gaus fitting

keV

Sensitivity

• T1/2 = log 2 e N T / dS

• e : efficiency

• N : Number of double beta nuclei

• T : Data taken time with year

• dS : mean value + 1.64 of Gaussian fitted area

(mean value is Q-value)

• T1/2 = 1.71x1019 year by 90% C.L (Preliminary)

Intrinsic radio-impurities

– coincidence candidates

1. 238U chain

214Bi : 3.27 MeV -decay214Po : 7.834 MeV -decay

– Lifetime of 214Po = 164.3 us– 190 keV Energy threshold

214Po – sidesubtraction

main

side

214Bi - spectrum

214Po – spectrum

214Po - decay

- Quanching factor = 804/7834 = 10.3%

- 4842 개 /75day = 65 개 /day

Q=3.27MeV

Q=7.834MeV

keV

214Po - half-life

s

T 1/2 = 235.9us * log(2) = 163.5 us

T 1/2 = 163.7us

s

2. 232Th chain

212Bi : 2.254 MeV -decay 212Po : 8.784 MeV -decay

– Lifetime of 212Po = 299 ns– 1ch = 2ns

1x

3x

channel

212Bi - spectrum

212Po - spectrum

212Po - decay

- Quanching factor = 940/8784 = 10.7%

- 281 개 /75day = 3.8 개 /day

Q=8.784MeV

Q=2.254MeV

212Po - half-life

T 1/2 = 422.9ns * log(2) = 293.1 ns

T 1/2 = 299ns

ns

Summary

1. TMSN40% by 500MHz FADC (75 days)

T1/2 = 1.71x1019 year by 90% C.L

2. 214Po - decay -> 65 개 /day

3. 212Po - decay -> 3.8 개 /day

4. World limit = 2~5x1017 year by 1952

Plan

• G4 simulation – intrinsic radio-impurities -> 238U, 232Th decay chains • Background reduction• Nd2EH and Zr2 EH study

• 2 DB study