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The Recent Status of KIMS Group and New Plan
Li Xin (Tsinghua University)KIMS collaboration
Aug. 28th, 2006
KIMS Collaboration
Korea:Seoul National University (Dark Matter Research Center)Sejong UniversityKyungpook National UniversityYonsei UniversityEwha Womans University
China:IHEP (Institute of High Energy Physics)Institute of Physics Academia Sinica (Taipei)Tsinghua University
USA:University of Maryland
Yangyang
3.5 hours by car
Yangyang Lab (Y2L)
Seoul National University
(SNU, DMRC)
Kyungpook National
University (KNU)
JumBong Mt. 1424m 750 m
Entrance 250m
Length 2km
Experimental
hall 50m DepthDepth Minimum 700 m Minimum 700 m
TemperatureTemperature 20 ~ 25 20 ~ 25 ooCC
HumidityHumidity 35 ~ 60 % 35 ~ 60 %
Rock contents Rock contents 238238U less than 0.5 ppmU less than 0.5 ppm 232232Th 5.6 A 2.6 ppmTh 5.6 A 2.6 ppm
4040K 270 A 5% ppmK 270 A 5% ppm
Muon flux Muon flux 4.3 4.3 x 10x 10-7-7 /cm /cm22/s ( 1 x 10/s ( 1 x 10-2-2 /cm /cm22/s )/s )
Neutron flux Neutron flux 8 8 x 10x 10-7-7 /cm /cm22/s ( 1.4 x 10/s ( 1.4 x 10-3-3 /cm /cm22/s )/s )222222Rn in airRn in air 1 1 pCi/liter ( 4 pCi/liter )pCi/liter ( 4 pCi/liter )
Gneiss (2 Gyr )
1000 mwe
KamiokaGran Sasso
Sudbury
CheongpyungOto
Yangyang, Soudan
HPGe detector measurement
Active detectors:
Muon DetectorNeutron Monitor Detector CsI (Tl) crystal
Passive shielding:
Mineral Oil: 30cmLead: 15cmPE: 5cmCopper: 10cm
CsI (Tl) crystal Production of CsI powderProduction of CsI powder
CsOH solution(50%)
Evaporation
Conversion to CsOH solution
Purification of Cesium salt solution
Digestion
Waste 2
Waste 1
Quartz
Pollucite Ore
Carbonization
Cs2CO3 Solution
Filtration
CsHCO3 +HX
Pure technical Cs Salts
CsOH solution + HX
High Purity Cs Salts
Cs Metal
• High light yield
• Pulse shape discrimination
• Easy to get large mass with an affordable cost
•Internal background due to 137Cs, 134Cs, 87Rb
Best available Crystal at Market70cpd
Powder Selection20cpd
Cs137 Reduction Using Pure water14cpd
Rb87 Reduction by Re-crystallization
6cpd
Reduction of internal background
Pulse shape discrimination
Nuclear recoil rate
Dark matter density at the solar system rD = 0.3 GeV c-2 cm -3
Use annual average parametersV0 = 220 km s-1, VE = 232 km s-1, VEsc = 650 km s-1
Limit curve
100kg 10 cpd100kg 1 cpd100kg 0.1cpd/1t 1cpd1t 0.1 cpd
PROSPECT
One ton CsI (Tl) !
Ultra-low Energy threshold HPGe detector experiment
5g Ge
1cpd
Expected threshold: ~100eV
Motivation Current weapon: 5g prototype Ge detector16.94kg CsI(Tl) veto detector
Target (<10GeV)
Current lowest threshold: 500eV (CRESST)
CsI noise reduction
Time coincidence between HPGe and CsI
i ii
ii
I tt
I
PSD parameter:
Threshold ~ 10keV
( ) 131.419
( ) 160.646
ns
n ns
Veto conditionRed: background file, Green: neutron file, Blue: Gamma file
Background level
Energy region: threshold(300eV) ~ 100keV
Blue: after veto, Red: before veto
Average veto efficiency ~ 60%
Average background level ~ 40 cpd
Threshold
Threshold: 300eV
Veto efficiency distribution
Energy region: threshold(300eV) ~ 100keV (1keV/bin)
Blue: gamma files, Green: neutron files, Red: background files
Main origin of background: neutron
Summary and future planCsI (Tl) crystal for WIMP search
► 826 kg days data with 3 modules of 6cpd crystals was analyzed We can draw
competitive limit to other crystal detector experiments.
► Low Temperature running was done Analysis is on going.
► New crystal has arrived Cs137 was reduced
► 2~4cpd level Increase of light output
ProspectProspect
Summary and future planULE-HPGe detector for WIMP search
ProspectProspect► Increase the mass of the
detector (aim: 1kg, detector array) 4×5g ULE-HPGe detector
will arrive Y2L next spring.
► Neutron shielding Background is mainly from
environmental neutron.
► Neutron recoil experiment Neutron recoil experiment
will be carried out in CAEA this Oct. to measure the quenching factor in low energy region more accurately.