1. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak Current Limit of WIMP search with CsI(Tl) crystal in KIMS 이현수 *, 곽정원, 김상열, 김선기, 김승천, 명성숙, 방형찬, 양혜영, 이명재, 이주희, 이직, 최정훈 ( 서울대 ) 김영덕, 이정일 ( 세종대 ) 김 홍주, 소중호, 양성철 ( 경북대 ) 권 영준, 황 명진 ( 연세대 ) 박일흥, 한인식 ( 이화여대 ) 서은숙, 이무현 ( Univ. of Maryland) J. J. Zhu, D. He, Q. Yue (Tsinghua University) J. Li (IHEP)

2. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak KIMS experiment Purpose : Search Dark matter ( Weakly Interacting Massive Particle ) 1. Find unknown components of our Universe - 73% Dark Energy(???) + 23% Dark matter(?) + 4% Known matter(…) 2. Probe various theories of Super Symmetry Particle Required 1. Developed low background CsI(Tl)detector - Successful reduction of the internal background of CsI(Tl) crystal 2. Deep underground experimental hall to avoid cosmic ray and induced backgrounds 3. Constructed a shield composed of pure materials and a muon detector with full coverage of solid angle.

3. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak Underground experimental hall in Yangyang JumBong Mt. 1424m 750 m Entrance 250 m Experimental hall 50m DepthMinimum 700 m Temperature20 ~ 25 o C Humidity35 ~ 60 % Rock contents 238 U less than 0.5 ppm 232 Th 5.6 A 2.6 ppm 40 K 270 A 5% ppm Muon flux 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 ) 222 Rn in air1 pCi/liter ( 4 pCi/liter ) Gneiss (2 Gyr ) HPGe detector measurement

4. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak WIMP search experiments Gaitskell’s summary talk IDM2004

5. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak Best available Crystal at Market Powder Selection Cs137 Reduction Using Pure water Rb87 Reduction by Re-crystallization CsI Crystal detector CsI(Tl) Crystal 8x8x30 cm 3 (8.7 kg) 3” PMT (9269QA) Quartz window, RbCs photo cathode 4~5 Photo-electron/keV DAQ 500MHz Home Made FADC 5 photo-electron within 2μsec trigger condition total 32μsec window Data taking with 3 crystals – 24 kg - 5.5cpd background level Produced 600 kg of More purified powder - use 18 M  pure water - More re-crystallization - Expected Less than 2cpd background level - Current shield can house up to 250kg crystal Typical Fe55 Signal

6. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak CsI Data Taking  Data for WIMP search  430 kg days for 8x8x30 cm 3 crystal of 14 cpd background level 2004 spring  237 kg days for 8x8x23 cm 3 crystal of 6 cpd background level 2004 summer  679 kg days for 24 kg CsI(Tl) crystal of 6 cpd background level (~ now)  MC data using Geant4 simulation  Calibration data Neutron data from Neutron calibration facility Reference distribution for recoil events 57 Co ( 122.06 keV  ) and 55 Fe (5.9 keV) Compton data Check Surface events, Single photon calibration 137 Cs ( 661.657 keV  ) Compton data Reference distribution for  events

7. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak  Dark matter density at the solar system   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  Differential rate per unit detector mass ,  Limit curve Calculation

8. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak Pulse Shape Discrimination (Mean time method)

9. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak Limit curve with 237 kg days data ( 2004.10. ) Background level  Recoil energy threshold > 20 keV  Used measured quanching factor of Recoil energy

10. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak Analysis with 679 kg days data  CsI(Tl) Crystal detectors 0406 crystal - 6.7 kg 0501A and 0501B crystals - 8.7 x 2 kg -Total 24 kg Crystal ( 5 ~ 6 cpd internal background )  log(Mean Time) spectrum depend on # of P.E  Calibration  Gamma reference & B.G. use Charge sum of Am241 peak (59.54keV)  Neutron reference -Cluster charge was normalized with cluster charge of B.G.  Analysis cuts -Optimized with Gamma reference data -To avoid electrical noises and abnormal events

11. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak 0501B Crystal – w/o Quartz light guide ~ 4.7 p.e./keV2-3keV3-4keV4-5keV5-6keV6-7keV7-8keV 8-9keV9-10keV10-11keV Preliminary

12. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak 0501A Crystal – with Quartz light guide ~ 3.7 p.e./keV2-3keV3-4keV4-5keV5-6keV6-7keV7-8keV 8-9keV9-10keV10-11keV Preliminary

13. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak Module dependency 04060501A0501B Data# of p.e.Size of CrystalQuartz wave guide 0406 237 kg days 4.98x8x23 cm 3 6.7 kgW 0501A 263 kg days 3.78x8x30 cm 3 8.7 kgW 0501B 179 kg days 4.78x8x30 cm 3 8.7 kgW/O S B SS BB cut

14. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak Limit curve using All data Weighted sum more # of p.e., better PSD Larger size, less surface effects Preliminary

15. KPS @ Iwha Womans University 2005/04/22 Hyunsu Lee & Jungwon Kwak Future plan  600 kg of 2cpd background level powder was produced - Small size crystal growing has done  Improve # of p.e. - Light shielding, reflector - Quartz window  Need more study - Size dependency - Energy calibration - Surface effect Preliminary