KPS Chonbuk University 2005/10/22 HYUNSU LEE Status of the KIMS dark matter search experiment with CsI(Tl) crystals Hyun Su Lee Seoul National University (For KIMS Collaboration)

KPS Chonbuk University 2005/10/22 HYUNSU LEE KIMS experiment Purpose – WIMP Dark Matter Search Required  Cross section of WIMP is too small : less than cm 2  As possible as low background environments is needed  Deep underground experimental hall to avoid cosmic ray and induced background  Shielding with pure materials to avoid environment background from radioisotope  Developed low background CsI(Tl) detector  WIMP interact with nucleus of target  Improve PSD capability to extract nuclear recoil from data (mainly electron recoil)  Increasing photo-electron yields  Recoil Energy is very small  Low energy threshold

KPS Chonbuk University 2005/10/22 HYUNSU LEE Korea Middleland Power Co. Yangyang Pumped Storage Power Plant Yangyang Underground Laboratory Minimum depth : 700 m / Access to the lab by car (~2km) (Upper Dam) (Lower Dam) (Power Plant)

KPS Chonbuk University 2005/10/22 HYUNSU LEE Shielding for External background reduction

KPS Chonbuk University 2005/10/22 HYUNSU LEE CsI(Tl) Crystal detector CsI(Tl) Crystal 8x8x30 cm 3 (8.7 kg) 3” PMT (9269QA) Quartz window, RbCs photo cathode 4~6 Photo-electron/keV DAQ 500MHz Home Made FADC 5 photo-electron within 2μsec trigger condition total 32μsec window 3 crystal modules about 6cpd level was already made Best available Crystal at Market Powder Selection Cs137 Reduction Using Pure water Rb87 Reduction by Re-crystallization

KPS Chonbuk University 2005/10/22 HYUNSU LEE DATA Data for WIMP search (826 kg days data are used to this analysis)  SET1 (July 2004 ~ Sep. 2004)  0406 Crystal (8x8x23 cm 3 ) – 237kg day (w/o quartz block – 5.5PE/keV)  SET3 (Feb. 2005~May. 2005)  0501A Crystal(8x8x30cm 3 ) – 202kg day (w/o quartz block – 4.5PE/keV)  0501B Crystal(8x8x30cm 3 ) – 386kg day (w quartz block – 3.7PE/keV)  SET6 (Aug. 2005~Oct. 2005)  Low Temperature Running (~0 o C) with 3 crystals (~6cpd level)  Now we are taking Compton events  700~900kg days data (Analysis is on going) MC data using Geant4 simulation Calibration data  Neutron data from Neutron calibration facility  Reference distribution for recoil events  - equivalent to 2000 kg days of underground data  Am241(59.5keV)  Energy Calibration  137Cs ( keV ) Compton data  Reference distribution for γ events  equivalent to 3600 kg days of underground data  Cut efficiency calculation

KPS Chonbuk University 2005/10/22 HYUNSU LEE 46 o CsI BC501a LSC 90 o 17.4 o n Am/Be Tag γ(4.4MeV) to measure TOF and energy of neutrons Calibration of Neutron Neutron Calibration Facility at SNU Compton events of WIMP search crystal was taken with Cs137 source in the underground lab Neutron events of small size crystal was taken with neutron source at SNU Compton of small size crystal was taken for comparison Compton at SNU Neutron at SNU 4-5 keV Compton at underground

KPS Chonbuk University 2005/10/22 HYUNSU LEE Event Selection to reject PMT related backgrounds The biggest cluster charge (PE) Mean charge of cluster (PE) Cs137 Compton Data Mean charge of cluster (PE) PMT Background Energy(keV) Energy(keV) Energy(keV)Energy(keV) Equivalent to ~167 kg days underground data ~less than 0.01CPD

KPS Chonbuk University 2005/10/22 HYUNSU LEE Cut Efficiency Compton at underground Compton at SNU Neutron at SNU The difference of efficiencies is taken into account as systematic error. Really we conservatively calculate efficiency

KPS Chonbuk University 2005/10/22 HYUNSU LEE Extraction of Nuclear recoil events 3 ~4 keV 10~11 keV9~10 keV 8~9 keV 7~8 keV6~7 keV 5~6 keV 4~5 keV Background Data Gamma Calibration Neutron Calibration

KPS Chonbuk University 2005/10/22 HYUNSU LEE Nuclear Recoil Rate 241 Am energy distribution solid line for MC and dotted points for data Simulated energy distributions of WIMP for different masses 20 GeV,50 GeV,100 GeV,1 TeV Log mean time distribution of background events are fitted to distributions of Compton events and neutron events

KPS Chonbuk University 2005/10/22 HYUNSU LEE Limit curve   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

KPS Chonbuk University 2005/10/22 HYUNSU LEE Low Temperature(~0 o C) Operation To Avoid PMT related backgrounds Photo-electron yield increasing MT increasing We had 2 month data  Now we are taking Compton events Number of PE Log(MT) Normal Operation Low Temp. Operation Normal Operation Low Temp. Operation Background Spectrum without cuts Energy(keV) CPD Fe55 Calibration Improve PSD powder Decrease background

KPS Chonbuk University 2005/10/22 HYUNSU LEE New Crystal arrived We made further Cs137 reduced powder than now using crystals  ~2cpd reduction is expected  Small size crystal(0504) was made and tested At last month, two full size(8.7kg) crystal was arrived  Cs137 amounts was measured with HPGe detector  Similar with expectation (~2cpd reduction will be possible) One more crystal was ready in beijing 200kg powder(same quality) will be sent  2crystals/1month can be possible Arrived date NameB.G. LevelSizePE YieldCompany 2004/ CPD8x8x23 cm kg5.5/keVShanghai 2005/010501A6CPD8x8x30 cm kg4.5/keVShanghai 2005/010501B6CPD8x8x30 cm kg4.5/keVShanghai 2005/040504~4CPD5x5x23 cm kg6.8/keVBeijing 2005/100510A~4CPD8x8x30 cm kg?Beijing 2005/100510B~4CPD8x8x30 cm kg?Beijing

KPS Chonbuk University 2005/10/22 HYUNSU LEE Summary & Prospects 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 was arrived  Cs137 was reduced  2~4cpd level  Increase of light output Prospect Increasing of PSD power can improve sensitivity KIMS 826 kg day

KPS Chonbuk University 2005/10/22 HYUNSU LEE

KPS Chonbuk University 2005/10/22 HYUNSU LEE Crystal Dependence of Mean Time 20~25 PE events selected A0501B