Transcript dmrc.snu.ac.kr

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)
2)
3)
4)
5)
Why high-Z loaded liquid scintillator?
Spin Dependent WIMP Search with nuclear excitation
Double beta decay with Tin
R&D status and plan for the Tin loaded LSC
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 :
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)
DE=25keV; f=0.5, 50keV;0.2, 100keV;0.07 at
Mw= 100GeV
SD WIMP with nuclear excitation
Iso. Abun.(%)
I127
100
Cs137 100
Ho165 100
Fe57
2.1
Kr83 11.5
Sn119 8.6
<=======
Te125 7.0
Xe129 26.4
Gd157 15.7
Yb173 16.2
W183 14.3
DE t(ns) MM12 R(Mw=100Gev)
57.6 1.9 0.1
0.27
81
6.3 0.02 0.01
94.7 0.06 2.2
1.4
14.4 98
0.06 0.42
9.4 147 0.08 0.3
23.9 18 0.11 0.77
35.5
39.6
54.5
78.6
46.5
1.5
1.0
0.1
0.04
0.18
0.16 0.86
0.2
0.95
0.59 1.5
1.0
1.1
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,
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
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
2 nu double beta measurement