Tin loaded liquid scintillator for 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 excitation 3) Double beta decay with Tin 4) R&D status and plan for the Tin loaded LSC 5) 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 = R sdin /R sde = ¾ f (M M1 /,  p,n ) 2 (2J*+1)/(2J+1) /( 2J'(J'+1)),  p =2.79,  n =-1.91; Erec > 0keV threshold for sdin J*:excited state from J, J': SDE M M1 : M1 transition matrix elelment, Calculation from measured  M1 f : phase factor = Integral ( 1/v*dn/dv dv)  keV; f=0.5, 50keV;0.2, 100keV;0.07 at Mw= 100GeV

SD WIMP with nuclear excitation Iso. Abun.(%)  E t(ns) M M1 2 R(Mw=100Gev) I Cs Ho Fe Kr Sn <======= Te Xe Gd Yb W

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 : %  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 > 6x10 13  Sn-124 -> Te-124 : Q=2287 keV 0nu (>2.4x10 17 ), 2nu (>1.0x10 17 ) : 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)>2.4x10 18, 2+(1325)>2x10 18, 0+(1656)>2.2x10 18

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 (CH 3 (CH 2 ) 3 CH(C 2 H 5 )CO 2 ) 2 Sn ( 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.... P LAN ( 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 * 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; 10 7 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