PyungChang 2006/02/06 HYUNSU LEE CsI(Tl) crystals for WIMP search Hyun Su Lee Seoul National University (For The KIMS Collaboration)

PyungChang 2006/02/06 HYUNSU LEE Index CsI crystal & background reduction  Internal background & reduction  External background Our setup & data taking  Detector & DAQ  Calibration & Data Analysis  Limit on SD & SI interaction  Preliminary results of low temperature(~0 degree) operation Summary

PyungChang 2006/02/06 HYUNSU LEE Advantage High light yield ~60,000/MeV Pulse shape discrimination Easy fabrication and handling High mass number(both Cs and I) Relatively easy to get large mass with an affordable cost Disadvantages Emission spectra does not match with normal bi-alkali PMT => Effectively reduce light yield 137 Cs(  1/2 ~30y), 134 Cs(  1/2 ~2y) may be problematic Why CsI(Tl) Crystal ? CsI(Tl) NaI(Tl) Photons/MeV ~60,000 ~40,000 Density(g/cm3) Decay Time(ns) ~1050 ~230 Peak emission(nm) Hygroscopicity slight strong

PyungChang 2006/02/06 HYUNSU LEE Background of CsI Crystal 137 Cs (artificial)  serious background at low energy 134 Cs (artificial+ 133 Cs(n,gamma)) 87 Rb (natural)  Hard to reject  reduction technique in material is known Single Crystal (~10 kg) ~10keV 87 Rb 1.07 cpd/1ppb HR ICP-MASS 137 Cs 0.35 cpd/1mBq/kg HPGe 134 Cs 0.07 cpd/1mBq/kg HPGe Pollucite( raw material for Cs ) contains < 8 mBq/kg of 137 Cs 137 Cs : 10 mBq/kg 134 Cs : 20 mBq/kg 87 Rb : 10 ppb 87 Rb 137 Cs 134 Cs keV CPD Geant Simulation

PyungChang 2006/02/06 HYUNSU LEE Internal Background Reduction Normal Water Ultra pure Pure water CsI solubility in water is very high. Recrystallization is done at slightly lower temperature from saturation point. 10 ppb powder  ~ 1 ppb (< 1.1cpd) Rb87 Reduction Cs137 Reduction Water is main source of Cs137 It was reduced by using purified water

PyungChang 2006/02/06 HYUNSU LEE Backgrounds of 0406 crystal ‘Pure water’ Recrystallization to reduce Rb mBq/kg mBq/kg ppb ~6 10keV

PyungChang 2006/02/06 HYUNSU LEE U/Th/K in PMT with gamma spectrum using HPGe detector

PyungChang 2006/02/06 HYUNSU LEE Components of external backgrounds

PyungChang 2006/02/06 HYUNSU LEE Further reduction of Cs137 with ‘ultra pure’ water ~ 2mBq/kg of 137Cs expected

PyungChang 2006/02/06 HYUNSU LEE Muon induced backgrounds Coincident time between CsI and MUD Coincident events in CsI crystal Coincident events in neutron detector DataSimulation Muon Muon Muon Induced Muon Induced We can identify muon induced neutron events from MUD-ND coincidence. It help us understand the muon induced neutron background in CsI crystal with Simulation

PyungChang 2006/02/06 HYUNSU LEE Crystal Accommodation Arrived date NameB.G. Level SizePE YieldOperationCompany 2004/ CPD8x8x23 cm kg4.8/keVFinishedShanghai 2005/010501A6CPD8x8x30 cm kg4.3/keVRunningShanghai 2005/010501B6CPD8x8x30 cm kg4.5/keVRunningShanghai 2005/040504~4CPD5x5x23 cm kg5.8/keVBeijing 2005/100510A~4CPD8x8x30 cm kg5.5/keVRunningBeijing 2005/100510B~4CPD8x8x30 cm kg5.2/keVRunningBeijing 2005/110511~4CPD8x8x30 cm kg?PreparedBeijing 2005/120512~4CPD8x8x30 cm kg?PreparedBeijing 2006/010601~4CPD8x8x30 cm kg?PreparedBeijing Now growing the crystal is on process ~ 1 crystal/month

PyungChang 2006/02/06 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)  SET3 (Feb. 2005~May. 2005)  0501A Crystal(8x8x30cm 3 ) – 202kg day (w/o quartz block)  0501B Crystal(8x8x30cm 3 ) – 386kg day (w quartz block)  SET6 (Aug. 2005~Oct. 2005)  Low Temperature Running (~0 o C) with 3 crystals (~6cpd level)  ~1000 kg days data (Analysis is on going)  SET8 (Dec. 2005~)  Low Temperature Running with 4 full size crystals (two of ~6cpd and two of ~4cpd) 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 in room temperature  Low temperature running is on process  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

PyungChang 2006/02/06 HYUNSU LEE 300 mCi Am/Be source  neutron rate 7 x 10 5 neutrons /sec  a few 100 neutrons/sec hit 3cmX3cm crystal  Quenching factor of Recoil Energy Take Neutron calibration data PSD check – Quality factor 46 o CsI BC501a LSC 90 o 17.4 o n Am/Be Tag γ(4.4MeV) to measure TOF and energy of = 10 keV 137 Cs Compton Neutron Recoil Background data Neutron calibration facility in SNU

PyungChang 2006/02/06 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

PyungChang 2006/02/06 HYUNSU LEE Nuclear Recoil Rate (826 kg days data) (a) 241 Am energy distribution solid line for MC and dotted points for data (b) Simulated energy distributions of WIMP for different masses in the case of SI interaction 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

PyungChang 2006/02/06 HYUNSU LEE WIMP Proton Cross Section WIMP Nucleus Scattering Spin Independent Spin Dependent ρ χ =galatic halo density v E =earth velocity in galatic frame v 0 =sun velocity in galatic frame

PyungChang 2006/02/06 HYUNSU LEE Spin Independent Limit   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

PyungChang 2006/02/06 HYUNSU LEE Spin dependent limit (Only use I) M.T.Ressell and D.J.Dean Phys. Rev. C 56 (1997) 535 Bonn A =0.395 =0.075 ProtonNeutron

PyungChang 2006/02/06 HYUNSU LEE Summary We successfully reduced the internal background of CsI crystal We are studying the external background We accommodate 60 kg full size crystals  Further production is on going ~ 1 (8.7kg) crystals/month speeds We have 826 kg days data in Room temperature  Partially reject DAMA 3 sigma region in SI limit We are taking data in low temperature (~0 degree)  We took ~2000 kg days WIMP search data  We try to calibrate neutron in the low temperature  We had done the low temp. setup in SNU last week.  Much better results expected

PyungChang 2006/02/06 HYUNSU LEE