Tin loaded liquid scintillatorfor the double beta decay experiment

Presented by H.J.Kim, KIMS Yonsei Univ, 10/23/2002

Workshop on Underground and Astropparticle Physics

Contents

1) Why high-Z loaded liquid scintillator?2) Spin Dependent WIMP Search with nuclear

excitation3) Double beta decay with Tin4) R&D status and plan for the Tin loaded LSC5) Summary and Prospect

Why high-Z loaded scintillator? Advantage a) Some high-Z can't be used for the good

scintillator. b) high-Z can be loaded to LS (>50% or more) c) Fast timing response (few ns) d) Low cost of LS, Large volume is possible e) U/Th/K reduction for LS is low and purification is known Disadvantage a) Bigger volume is necessary (C,H in LS, low

density) b) Moderate light output (~15% of NaI(Tl)) Available Technology : B, Li( 10%),Gd(1%), Pb(5%),Sn(10%) <- Commercial Yb,In(LENS, 10%) loading

High-Z loaded LS physics Spin dependent Inelastic WIMP search * => Only theoreticl ideas. Solar neutrino detection

LENS (under R&D) Reactor neutrino oscillation experiment Gd (<1%) loaded LSC Supernova neutrino detection Gd(<1%) SIREN (under R&D) Low energy neutrino detection (<~few MeV) Neutrino source experiment (R&D) Double beta decay Search *

=> New

Spin Dependent WIMP with nuclear excitation

M.Goodman and E.Witten PRD 31(1985)3059

J.Ellis et al. PLB 212 (1988) 375 RSD = Rsdin/Rsde

= ¾ f (MM1/,mp,n)2 (2J*+1)/(2J+1)

/(l2J'(J'+1)) ,mp=2.79, mn=-1.91; Erec > 0keV threshold

for sdin J*:excited state from J, J': SDE MM1: M1 transition matrix elelment,

Calculation from measured GM1

f : phase factor = Integral ( 1/v*dn/dv dv)

=25DE keV; f=0.5, 50keV;0.2, 100keV;0.07 at Mw= 100GeV

SD WIMP with nuclear excitationIso. Abun.(%) DE t(ns) MM1

2

R(Mw=100Gev) I127 100 57.6 1.9 0.1 0.27Cs137 100 81 6.3 0.02 0.01Ho165 100 94.7 0.06 2.2 1.4Fe57 2.1 14.4 98 0.06 0.42Kr83 11.5 9.4 147 0.08 0.3Sn119 8.6 23.9 18 0.11 0.77

<=======Te125 7.0 35.5 1.5 0.16 0.86Xe129 26.4 39.6 1.0 0.2 0.95Gd157 15.7 54.5 0.1 0.59 1.5Yb173 16.2 78.6 0.04 1.0 1.1W183 14.3 46.5 0.18 1.0 4.1

Double beta decay

0 nu double beta decay limit

Most stringent

Excited state transition

0 nu double beta evidence ??

Future DB experiment

Why double beta decay (DB) with Sn?

Purpose: Observation of 2nu at Sn-124 and setting most stringint limit on 0nu Sn-122,124 2nu,0nu DB. If we are lucky, we may be discover 0nu double beta decay.

It is important to study many DB source since theoretical prediction is diffcult in calculation

Sn 2-nu DB is not observed and 0-nu DB limit is very poor.

Theoretical predcition of 2-nu and 0-nu life time is as good as others.

Sn can be obtained with pure material : 99.999% 10% Sn LSC loading technology is available.

Sn DB limit Sn-122 -> Cd-122 : EC + beta+(0nu), Q=1922keV Sn-122 -> Te-122 : 2 0nu beta , Q=

366.2keV J.Fremlin and M.C.Walters, Proc. Phys. Soc. A65,

911 (1952) : 0nu limits > 6x1013

Sn-124 -> Te-124 : Q=2287 keV 0nu (>2.4x1017), 2nu (>1.0x1017) : J.A. Mccarthy, Phys.Rev. 90(1953) 853 Cloud chamber, 2.2g(95% enriched) Sn-124 Sn-124 -> Te-124 excited state transition limit Eric B.Norman, D.Meekhof, Phys. Lett.

195,126(1987) 110cm3 HPGe, LBL with shield, Sn 647g, 666 hour

data 2+(603)>2.4x1018, 2+(1325)>2x1018,

0+(1656)>2.2x1018

DB decay diagram of Nb,Zr,Cd and Sn

Limit of Sn 0nu and 2nu DB

Using Tin loaded LSC

Sn-LSC and characteristics * Tin loading : How much? * Light output * Attenuation length * Stability * n, gamma response Background * Sn background

* LSC background * External background Enrichment? : Sn-124 (5.79%)->95% ; 3000$/g

Tin loading study

Technoly is commercally available but not in public Tin compound 1) 2-Ethyl hexanoate (144g/mole), Tin 15% w 50%

loading (CH3(CH2)3CH(C2H5)CO2)2Sn ( FW405) =>

Quanching 2) Tetramethyl-tin (40%w50%) :

flammable,expensive 3) Tetrabutyl-tin (19%w50%) 4) Others? LS : Solvent+Solute * Solvent ; PC, 1,2-MN, o-,p-Xylene, Tolune,

Benzene.. * Solute ; POP, BPO, PBD, Butyl-PBD, Naphthalene.. * Second-solute ; POPOP, M2-POPOP, bis-MSB...

Tin loading

Tin loading (TBSN 50%->20%Sn)

Tin loading

Tin background study

HPGe measuremnet of TBSN (RND), TBSN (SR) and SnCl4 (RND)

TBSN test with 100% HPGe detector at CPL : 1.0 liter

1 week data taking. TBSN results : No extra peak compare with

background, U,Th,K peaks are consistent with the background within statistical errors. Tl-208 (2600keV peak) ; Cris. Crystal : 0.42mBq, TBSN(RND) 0.45mBq, TBSN(SR) : 0.44mBq. (about 10% statistal errors for measurements)

Sn-124, Sn-122 0,2nu DB limit * World best limit on Sn124 (E.Norman PLB 195,1987) 110cm3 HPGe, LBL with shield, Sn 647g, 666 hours About 1500events/keV at 603 keV energy Test of TBSN for a week at CPL , Preliminary results 450cm3 HPGe, 140 hours , 1.0liter TBSN : 400g of Sn About 15events/keV at 603 keV energy, full peak efficiency = 2-6%

* Preliminary Sn-124 0,2nu DB limit(68% CL) 2+ (603keV) 3.8x10^18 year (4.0x10^19 year) 0+ (1156) 1.1x10^19 year ( 2nu theory :

2.7x10^21) 0+ (1326) 1.3x10^19 year (2.2x10^18 year)* Sn-122 EC+beta+ decay ; 1.5x10^18 year

( 6.1x10^13)

Geant4 simulation for HPGe efficiency

Sn-124 DB excited level transition

Sn-112 EC+beta+ excited level

Summary * high-Z loaded LS can be good candidate for the underground experiment. * There are many physics opportunity with high-Z loaded LS, any new ideas? * Tin loaded LSC can be used for the double beta experiment. (up to 40% Sn loading) * Already we achieved world the best sensitivity

for Sn-124, Sn-122 excited level decay and hope to find 2nu double beta as well as 0nu double

beta decay mode. * We need theoreticl help on DB prediction and other physics ideas.

Plan * High-Z loaded LS study more : Gd, Zn ....

PLAN ( If funding and manpower is allowed) * Coincidence experiment with Tin loaded LSC(1 liter)

+ HPGe : Almost background free and will improve sensitivity one or two order => This winter * 30-50 liter of Tin loaded LSC in prototype shielding at CPL. Sensitivity to observe 2nu DB mode. => Next summer * 1-10 ton of Tin loaded LSC or enrichment : This will allow us to compete with world next generation DB experiment ! => Future underground experiment

0 nu double beta decay

Gamma level diagram of Te-124

TBSN with HPGe detector

Limit of Sn

SD with Sn-119 * Advantage a) 24keV excitation + 20ns decay time b)100ns window; 107 random bg reduction -> almost background free

* Disadvantage a) Detection of Sn recoil energy with

quanching b) natural abundance 8.6% (enrichment?)

* Study needed a) Detail study of rate estimation with

threshold b) Recoiled Sn quanching in LSC c) Background study

2 nu double beta measurement