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.