1. The Recent Status of KIMS Group and New Plan Li Xin (Tsinghua University) KIMS collaboration Aug. 28th, 2006

2. KIMS Collaboration Korea: Seoul National University (Dark Matter Research Center) Sejong University Kyungpook National University Yonsei University Ewha Womans University China: IHEP (Institute of High Energy Physics) Institute of Physics Academia Sinica (Taipei) Tsinghua University USA: University of Maryland

3. Yangyang 3.5 hours by car Yangyang Lab (Y2L) Seoul National University (SNU, DMRC) Kyungpook National University (KNU)

4. JumBong Mt. 1424m 750 m Entrance 250m Length 2km Experimental hall 50m Depth Minimum 700 m Temperature 20 ~ 25 o C Humidity 35 ~ 60 % Rock contents 238 U less than 0.5 ppm 238 U less than 0.5 ppm 232 Th 5.6 A 2.6 ppm 232 Th 5.6 A 2.6 ppm 40 K 270 A 5% ppm 40 K 270 A 5% ppm Muon flux 4.3 x 10 -7 /cm 2 /s ( 1 x 10 -2 /cm 2 /s ) 4.3 x 10 -7 /cm 2 /s ( 1 x 10 -2 /cm 2 /s ) Neutron flux 8 x 10 -7 /cm 2 /s ( 1.4 x 10 -3 /cm 2 /s ) 8 x 10 -7 /cm 2 /s ( 1.4 x 10 -3 /cm 2 /s ) 222 Rn in air 1 pCi/liter ( 4 pCi/liter ) Gneiss (2 Gyr )

5. 1000 mwe Kamioka Gran Sasso Sudbury Cheongpyung Oto Yangyang, Soudan

6. HPGe detector measurement Active detectors: Muon Detector Neutron Monitor Detector CsI (Tl) crystal Passive shielding: Mineral Oil: 30cm Lead: 15cm PE: 5cm Copper: 10cm

7. CsI (Tl) crystal Production 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 Cs 2 CO 3 Solution Filtration CsHCO 3 +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 137 Cs, 134 Cs, 87 Rb

8. Best available Crystal at Market 70cpd Powder Selection 20cpd Cs137 Reduction Using Pure water 14cpd Rb87 Reduction by Re-crystallization 6cpd Reduction of internal background

9. Pulse shape discrimination Nuclear recoil rate  Dark matter density at the solar system r D = 0.3 GeV c -2 cm -3  Use annual average parameters V 0 = 220 km s -1, V E = 232 km s -1, V Esc = 650 km s -1 Limit curve

10. 100kg 10 cpd 100kg 1 cpd 100kg 0.1cpd/1t 1cpd 1t 0.1 cpd PROSPECT One ton CsI (Tl) !

11. Ultra-low Energy threshold HPGe detector experiment 5g Ge 1cpd Expected threshold: ~100eV Motivation Current weapon: 5g prototype Ge detector 16.94kg CsI(Tl) veto detector Target (<10GeV) Current lowest threshold: 500eV (CRESST)

12. CsI noise reduction Time coincidence between HPGe and CsI PSD parameter: Threshold ~ 10keV Veto condition Red: background file, Green: neutron file, Blue: Gamma file

13. 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

14. Veto efficiency distribution Energy region: threshold(300eV) ~ 100keV (1keV/bin) Blue: gamma files, Green: neutron files, Red: background files Main origin of background: neutron

15. Summary and future plan CsI (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 outputProspect

16. Summary and future plan ULE-HPGe detector for WIMP search Prospect ► 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.