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The Recent Status of KIMS Group and New Plan

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 University Kyungpook National University Yonsei University Ewha Womans University

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The Recent Status of KIMS Group and New Plan

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

  4. JumBong Mt. 1424m 750 m Entrance 250m Length 2km Experimental hall 50m Gneiss (2 Gyr )

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

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

  7. CsI(Tl) crystal Production of CsI powder Pollucite Ore • High light yield • Pulse shape discrimination • Easy to get large mass with an affordable cost • Internal background due to 137Cs, 134Cs, 87Rb Digestion Quartz Waste 1 Purification of Cesium salt solution Waste 2 Conversion to CsOH solution Evaporation Carbonization CsOH solution(50%) Filtration Cs2CO3 Solution CsOH solution + HX CsHCO3 +HX High Purity Cs Salts Pure technical Cs Salts Cs Metal

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

  9. Pulse shape discrimination Limit curve • Dark matter density at the solar system rD = 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 Nuclear recoil rate

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

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

  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. Threshold Background level Energy region: threshold(300eV) ~ 100keV Threshold: 300eV Average background level ~ 40 cpd Blue: after veto, Red: before veto Average veto efficiency ~ 60%

  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 output Prospect

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

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