kims : dark matter search experiment in koreadark.ft.uam.es/dsu2006/programme/talks/lee.pdf · 237...
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KIMS : Dark Matter Search Experiment in Korea
Jik LeeSeoul National University
For the KIMS Collaboration
DSU2006, Madrid
KIMS
H.C.Bhang, J.H.Choi, S.C.Kim, S.K.Kim, S.Y.Kim, J.W.Kwak, J.H.LeeH.S.Lee, S.E.Lee, J. Lee, S.S.Myung, H.Y.Yang
Seoul National University
Y.D.Kim, J.I. Lee, U.G. KangSejong University
H.J.Kim, S.C. Yang, J.H. SoKyungpook National University
M.J.Hwang, Y.J.KwonYonsei University
I.S.Hahn, I.H.ParkEwha Womans University
M.H.Lee, E.S.SeoUniv. of Maryland
J.LiInstitute of High Energy Physics
J.J.Zhu, D. He, Q.YueTsinghua University
Korea Invisible Mass Search
WIMP
SUSY model with R-parity conservation Neutralino : stable LSPweak interactions scale annihilation cross sectionproper relic density for dark matter
Neutralino:super-partner of neutral gauge and Higgs bosons
0214
01131211
01
~~~~χ~ HNHNWNBN +++=
⇒ Excellent CDM candidate
Direct WIMP SearchSignature : WIMP-nucleus elastic scattering
Signal by recoiled nucleus
scalar interaction
5 5( ) ( ) ( ) ( ) ....q qL f qq d q qμμχχ χγ γ χ γ γ= ⋅ + ⋅ +
spin-dep. interaction
2 2 232 ( 1)spin F rG m J Jσπ
= Λ +
1 ( )p p n na S a SJ
Λ ≡ < > + < >
224 ( )scalar r p nm Zf A Z fσπ
⎡ ⎤= + −⎣ ⎦
2A∝
SNU
Seoul
3.5hours by car
Yangyang
Korea Middleland Power Co.Yangyang Pumped Storage Power Plant
Yangyang Underground Laboratory
Minimum depth : 700 m / Access to the lab by car (~2km)
(Upper Dam)
(Lower Dam)
(Power Plant)
AdvantageHigh light yield ~60,000/MeV Pulse shape discrimination
Moderate background rejectionEasy fabrication and handlingEasy to get large mass with anaffordable cost
Good for AM study
DisadvantagesEmission spectra does not match with normal bi-alkali PMT
=> Effectively reduce light yield137Cs(τ1/2 ~30y) ,134Cs(τ1/2 ~2y) may be problematic
CsI(Tl) NaI(Tl)Photons/MeV ~60,000 ~40,000Density(g/cm3) 4.53 3.67Decay Time(ns) ~1050 ~230Peak emission(nm) 550 415Hygroscopicity slight strong
CsI(Tl) Crystal
∑∑=
i
ii
AtA
t
NaI(Tl)
CsI(Tl)
Pulse shape discriminationof gamma background
External backgrounds1. External gamma
Isotopes in surrounding materials (Rock)• Decay chain of U238 and Th232
• Isotopes (K40, …) • Rn222 in air Shielding structure made of pure and high Z materials Partially or fully distinguishable from WIMP signal by PSDN2 flowing to remove air contaminated by Rn222
2. Neutron backgroundIndistinguishable from WIMP signal (Nuclear recoil)• (α, n) reaction • Nuclear fission • Induced by cosmic muon ( E mean ~ 230 GeV )
- possible to veto with muon detector Neutron moderator made of material with High Hydrogen densityVeto system using Muon detector
KIMS
Neutron shield / Muon det.
Lead shield
Polyethylene
Copper shield
CsI(Tl) crystal
Mineral oil 30cm Pb 15cm : 30t
OFHC Cu 10cm : 3tPE 5cm
Muon Detector • 4π coverage muon detector : 28 channels • Liquid Scintillator(5%) + Mineral Oil (95%) = 7 ton • Measured Muon flux = 2.7 x 10 –7 /cm2/s• Position resolution : σx,y ~ 8 cm • Reconstructed muon tracks with hit information• Muon veto efficiency ~99.9%
1liter BC501A liquid scintillatorn/g separation using PSDE_vis > 300 keV
Neutron Monitoring Detector
neutronscandidates
Log10(Δt) Energy [MeV]
Muon induced neutrons
2 events of Muon induced neutron during 67.4 days ~ 0.03 counts/day/liter
neutronscandidates
Neutron Monitoring Detector214Bi β-decay 214Po α-decay
222Rn α-decay 218Po α-decay
Neutron Monitoring Detector(cont’d)
230Ra dominant contamination in 238U chain - 6.66 +- 0.27 cnts/liter/day – 1.5 x10-6 ppt of 230Ra level
232Th dominant contamination in 232Th chain - 0.32 +- 0.06 cnts/liter/day - 0.63 ppt of 232Th level
• All neutron events : alphas from internal sourcesNeutron rate < 1.8 cpd (90 % C.L. ) inside the shield
• Neutron rate outside the shield8 x 10 –7 /cm2/s ( 1.5 < E neutron < 6 MeV )
After subtracting internal background estimated from the data inside the shield
• Electrostatic alpha spectroscopy : 70 liter stainless container
• Use Si(Li) photodiode : 30 x 30 mm • Estimate 222Rn amount
with energy spectrum of a from 218Po & 214Po.• Photodiode calibration : 210Po, 241Am • 222Rn in air = 1 ~ 2 pCi/liter• Absolute efficiency calibration done with 226Ra
Radon Monitoring
Internal background of CsI Crystal
• 137Cs (artificial)– serious background at low energy
• 134Cs (artificial+133Cs(n,gamma))• 87Rb (natural)
– Hard to reject reduction technique in material is known
Single Crystal (~10 kg) background @ ~10keV
87Rb 1.07 cpd/1ppb 137Cs 0.35 cpd/1mBq/kg 134Cs 0.07 cpd/1mBq/kg
137Cs : 10 mBq/kg134Cs : 20 mBq/kg87Rb : 10 ppb
87Rb
137Cs
134Cs
keVkeV
CP
DC
PD
GeantGeantSimulationSimulation
From simulation
Reduction of Internal Background
• CsI solubility in water is very high.• Recrystallization reduces Rb87.• 10 ppb powder ~ 1 ppb (< 1.1cpd)
Rb87 ReductionRb87 Reduction
Cs137 ReductionCs137 Reduction• Water is main
source of Cs137• It was reduced by
using purified water
Further reduction of internal background
2mBq/kg 0.7 cpd internal background
New CsI powder produced with ultra pure water
Best available Crystal at MarketBest available Crystal at Market70cpd70cpd
Powder SelectionPowder Selection20cpd20cpd
Cs137 Reduction Using Pure waterCs137 Reduction Using Pure water14cpd14cpd
Rb87 Reduction by ReRb87 Reduction by Re--crystallizationcrystallization6cpd6cpd
Ultra Pure Water UsedUltra Pure Water Used4cpd4cpd
Reduction of Internal Background cont’ed
CsI(Tl) Crystal 8x8x30 cm3 (8.7 kg) 3” PMT (9269QA) Quartz window, RbCs photo cathode
4~6 Photo-electron/keVDAQ 500MHz Home Made FADC
5 photo-electron within 2μsec trigger conditiontotal 32μsec window
Name B.G. Weight Company
0406 6.7 kg
8.7 kg
8.7 kg
8.7 kg
8.7 kg
8.7 kg
0512 ~4CPD 8.7 kg beijing
8.7 kg
0605A ~4CPD 8.7 kg beijing
8.7 kg
0501A
shanghai
shanghai
shanghai
beijing
beijing
beijing
beijing
0501B
0510A
0510B ~4CPD
0511 ~4CPD
beijing
0601 ~4CPD
0605B ~4CPD
6CPD
6CPD
6CPD
~4CPD
Data taking with CsI(Tl)
Neutron calibration facility in SNU 300 mCi Am/Be source
neutron rate 7 x 105 neutrons /sec a few 100 neutrons/sec hit 3cmX3cm crystalQuenching factor of Recoil Energy Take Neutron calibration data PSD check – Quality factor
46o
CsIBC501a BC
501aBC501a LSC
90o17.4
o
n
Am/Be
Tag γ(4.4MeV)to measure TOF and energy of neutrons
@Energy = 4-5 keV137 Cs Compton Neutron Recoil
PSD discriminationMean time distribution
3~4 keV 4 ~5 keV
10~11 keV9~10 keV
8~9 keV7~8 keV6~7 keV
5~6 keV
Extraction of nuclear recoil events
)log(
)()(
><=
+
tx
xfNxfN iiiNR
iERERNR
Rate of nuclear recoil eventsLog mean time distribution of background events are fitted to distributions of Compton events and neutron events
Filled circle : w/o PMT noise cut
Open square : with PMT noise cut - efficiency corrected
Open circle : fitted the number of nuclear recoil events
55Fe energy distribution solid line for MC and dotted points for data
Simulated energy distributions of WIMP for different masses
20 GeV,50 GeV,100 GeV,1 TeV
Local WIMP density ~ 0.3GeV/cm3
Maxwellian velocity distribution with v ~ 270km/sLocal flux of WIMP ~ 100 GeV/mχ x 105/cm2/s
ρρχχ==galaticgalatic halo densityhalo density
vvEE=earth velocity in =earth velocity in galaticgalatic frameframe
vv00=sun velocity in =sun velocity in galaticgalatic frameframe
22
2(max) 2( )recoil x N
N
mE v m
m mχ
χ
=+
Recoil energy < 100 keVMeasured energy < 10 keV due to quenching
Interaction rate of WIMP
Dark matter density at the solar systemρD = 0.3 GeV c-2 cm -3
Use annual average parameters V0 = 220 km s-1, VE = 232 km s-1, VEsc = 650 km s-1
Spin Independent Limit
3879 kg days NAIAD - NaI(Tl) 237 kg days KIMS - CsI(Tl)4123 kg days DAMA - NaI(Tl)
KIMS First WIMP Limit
PLB 633(2006) 201In Feb. 2006
Spin dependent WIMP limit only with I
Pure proton casePure proton case Pure neutron casePure neutron case
Form factor and spin expectation value for Form factor and spin expectation value for ““II”” are obtained from are obtained from
““M.T.ResselM.T.Ressel and and D.J.DeanD.J.Dean PRC 56(1997) 535PRC 56(1997) 535
Spin independent
Spin dependent (pure proton)
• First physics result was published
• Various R&D run was done – About 4000 kg day data acquisited– With and without quartz block (5cm
thick) – 0 degree and Room temperature
operation– Analysis is ongoing
• Successfully reduce internal backgrounds of CsI(Tl) crystals
– 70 kg full size crystals(8x8x30cm3) are being prepared
– Mass production stage • 2 Crystal/Month growing is
possible
• With more than 100 kg crystals, we start to probe
– Annual modulation – SD+SI interaction search
WIMP search with CsI(Tl) crystalSummary & Prospects
ULE HPGe detector setup
CsI(Tl) crystal Compton veto
Built by TUDelivered to SNU
5g 1 cpd level detector Tested at Academia Cinica, Taiwanand delivered to SNU in Dec, 2004.
If successful upgrade to 1kg mass
Search for Low Mass WIMP
Collaboration with China and Taiwan
Double beta decay
(A,Z)(A,Z+1)
(A,Z+2)
(A,Z) (A,Z) --> (A,Z+2) +> (A,Z+2) + 22ββ +2+2νν
22
202/1/1
i
i
iv
iei emUm
mT
αββ
ββν
∑>=<
>∝<
Experimental search for Experimental search for DBDDBD
♦ Two approaches:
+ event shape reconstruction- low energy resolution- low efficiency
e-
e-
source
detector
detector
Source ≠ Detector
e-
e-
Source ≡ Detector(calorimetric technique)+ high energy resolution+100% efficiency- no event topology
sum electron energy / Q
Signature: shape of the two electron sum energy spectrum
1
10-2
10-6
R = 5%two neutrino DBD
continuum with maximum at ~1/3 Q
neutrinoless DBDpeak enlarged only by the detector energy resolution
low background- underground operation
- shielding- low radioactivityof materials
low energy resolution
2ν events canmask 0ν ones
♦ If you use the calorimetric approach
1. TMSN50% + STD Liquid scintillator124Sn 124Te + 2β−decay
2287keV
2. CaMoO4 Crystal 1.8x1.8x3.5 cm3
100Mo 100Ru + 2β−decay3034keV
T1/2 > 3.41x1019 yr at 90% C.L
Double beta decay R&D
10kg Mo10kg Mo--100 CaMoO100 CaMoO44
5-year runningT1/2 > 1x1025 yr at 68% C.L.
Present Present Best LimitBest Limit >>4.6x104.6x102323 yr @ 90% C.L.yr @ 90% C.L.
Other activitiesSummary and prospect
ULE HPGe detector for low mass WIMP searchCompton veto detector deliveredPrototype detector and shield is being soon
Cryogenic detector for low energy detectionFabrication and test of TES sensor on-going Need fast cycling of sample test for the TES optimization
Metal loaded liquid scintillator for 0νββ decayPilot experiment with 1 liter 50% Sn loaded LS encouraging resultStudy on internal background in progressLoading other element in progress
CaMoO4Test with a 50g crystal has been done encouraging resutR&D for growing optimization and background reduction in progress10kg crystal can be easily installed in the current WIMP search setup
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