The recent results from KIMS
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At Yangyang beach,
looking for something
in the swamp of particles
and waves.
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The recent results from KIMS
Seung Cheon Kim(Seoul National University)
for KIMS collaboration
Dark Side of the Universe 2011
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Dark matter ?
Rotation curve for Galaxy
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X-ray from Hot cluster
Parameters of CDM by WMAP Bullet cluster
Not visible, but gravitationally evident!
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Dark Side of the Universe 2011 4
If dark matter is WIMP,
It will deposit around 10 keV in the absorber!
But, its event rate will be very small.
Thermal signalScintillation, e-h pairProduced from nuclear Recoil(NR)
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Dark Side of the Universe 2011 5
KIMS experiment ?
CsI(Tl) scintillator
Well-known, widely-used technique
Large atomic number, Cs (133), I (127) Good for A2 scaling
High spin expectation value for proton Sensitive to SD interaction
Discrimination of nuclear recoilevents by PSD analysis
But, some inherent backgroundslike Cs134, Cs137, Rb87
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Detector design
One detector module : one CsI Crystal + 2 PMTs
PMT : 3” PMT (9269QA),Quartz window, RbCs photo cathode(green extended)
Crystal size: 8x8x30 cm3 (8.7 kg)(Beijing Hamamatsu Photon Techniques Inc.)
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Event window is 40µs.Digitized with 400MHz FADC
Am241 calibra-tion
13.9keV Np L X-ray17.8keV Np L X-ray20.8keV Np L X-ray26.35keV gammaCs, I X –ray escape59.54 gamma
5-6 p.e /keV
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Dark Side of the Universe 2011 7
Detector array
3 x 4 detector array
The total mass : 103.4 kg
Multiple hit events=> references for calibration
E of det10
Total E except det10
134Cs
134Ba
4+
3+4+
2+
2+
0+
1969.871643.281400.551167.93
604.70
0.0
E [keV]β-
27.3%2.50%70.1%0.033%
0.10%
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Neutron shield(30cm mineral oil)
Lead shield (15cm)
Polyethylene(5cm)
Copper (10cm)
CsI(Tl) ScintillatorNeutron detectorMuon detector(Neutron sheild)
KIMS Detector system
N2 gas flow inside the Cu shield8
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Experimental site
YangYang underground Lab(Y2L)
=>Located in Yangyang pumped storage power plant
=>700m minimum depth, muon flux : 2.7 x 10-7/cm2/s
=>accessible by car (tunnel~2km)
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4th WCU workshop 090908 10
Surface alpha (SA) background
Electron recoil events
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Dark Side of the Universe 2011 11
Study of SA events using Rn progeny contaminated crystal
PMTs
CsI(Tl) crystalA: Rn progeny contaminated ,exposed to Rn gas for 4 daysB: clean
Aluminum foil t=2m x 3 layers
A B
Sides are wrapped by teflon
SA
gamma
Tagged as alpha at B
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Dark Side of the Universe 2011 12
SA
NRER
Comparison of PSD parameter, logrmt10
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Event selection
Compton events
Period: September 2009 – August 2010 => 317.15 live days
PMT noise, muon-coincident events, tail events,multiple hit events rejected
tail events
Clean acryl boxPMT PMT
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Dark Side of the Universe 2011 14
The estimation of the NR events rate
Pdf = f0 x FNR + f1 x FSA + (1-f0-f1) x Fgamma
The posterior pdf for f0 & f1 is obtainedfrom Bayesian analysis method.
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Dark Side of the Universe 2011 15
The estimated NR event rates for 12 detectors
90 % limit68 % interval
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Dark Side of the Universe 2011 16
The overall NR events ratedet0, 8, 11 excludedTotal exposure: 24524.3 kg days
No meaningful excess of NR events is not observed !!!
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KIMS NR event rates & DAMA/LIBRA annual modulation amplitude
The annual modulation amplitude from DAMAÞ At 2-4keV, 0.0183±0.0022 counts/day/kg/keV
Þ At the corresponding energy range (3.6-5.8 keV) in KIMS, (QF for DAMA =0.08 adopted) The 90 % C.L limit is 0.0098 counts/day/kg/keV This is well below the DAMA modulation amplitude. Any scenario with Iodine for DAMA is not consistent with KIMS results !!!
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KIMS & DAMA in iDM model
For 70 GeV mass WIMP
CsI
Expected spectrum for iDM in KIMS detector=> M=70 GeV, δ=116keV, vesc=500 km/s, ve=235km/s, σ=0.93e-3 pb
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Dark Side of the Universe 2011 19
The new exclusion limits from KIMS
Spin-Independent interaction Spin-dependent proton interaction
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Dark Side of the Universe 2011 20
Annual modulation study
2 year of data have been obtained in the stable conditions.
Modulation analysis on going- w/o PSD- 2keV threshold
Stability of temperature, gain etc. has been monitored
Low energy contribution from Cs-134, the time varying background
Multiple hit events
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Dark Side of the Universe 2011 21
Summary
24524.3 kg days data was analyzed.
Surface alpha background were identified.
No meaningful excess of NR events were found.
Our 90 % limit for NR events is well below the amplitude observed by DAMA/LIBRA, disfavoringany Iodine interpretation.
New improved exclusion limits for WIMP-nucleon interaction were presented.
Annual modulation analysis results will be done soon.
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Dark Side of the Universe 2011 22
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Nothing found yet…