1. 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

2. 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

3. 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

4. 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

5. SD WIMP with nuclear excitation Iso. Abun.(%)  E t(ns) M M1 2 R(Mw=100Gev) I127 100 57.6 1.9 0.1 0.27 Cs137 100 81 6.3 0.02 0.01 Ho165 100 94.7 0.06 2.2 1.4 Fe57 2.1 14.4 98 0.06 0.42 Kr83 11.5 9.4 147 0.08 0.3 Sn119 8.6 23.9 18 0.11 0.77 <======= Te125 7.0 35.5 1.5 0.16 0.86 Xe129 26.4 39.6 1.0 0.2 0.95 Gd157 15.7 54.5 0.1 0.59 1.5 Yb173 16.2 78.6 0.04 1.0 1.1 W183 14.3 46.5 0.18 1.0 4.1

6. Double beta decay

7. 0 nu double beta decay limit Most stringent Excited state transition

8. 0 nu double beta evidence ??

9. Future DB experiment

10. 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.

11. 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

12. DB decay diagram of Nb,Zr,Cd and Sn

13. Limit of Sn 0nu and 2nu DB

14. 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

15. 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...

16. Tin loading

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

18. Tin loading

19. 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)

20. 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)

21. Geant4 simulation for HPGe efficiency

22. Sn-124 DB excited level transition

23. Sn-112 EC+beta+ excited level

24. 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.

25. 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 * 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

26. 0 nu double beta decay

27. Gamma level diagram of Te-124

28. TBSN with HPGe detector

29. Limit of Sn

30. 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

31. 2 nu double beta measurement