For the KIMS Collaboration Status of KIMS S.S. Myung (SNU) For the KIMS Collaboration Results from 4 crystal array Status of 12 crystal array

KIMS Collaboration H.C.Bhang, J.H.Choi, D.W.Kim, S.C.Kim, S.K.Kim, J.H.Lee,H .S.Lee, S.E.Lee, J. Lee, S.S.Myung Seoul National University U.G.Kang, Y.D.Kim, J.I. Lee Sejong University H.J.Kim, J.H.So, S.C.Yang Kyungpook National University M.J.Hwang, Y.J.Kwon Yonsei University I.S.Hahn Ewha Womans University Y.H.Kim, K.B.Lee, M. Lee KRISS J.Li Institute of High Energy Physics D. He, X.Li, Q.Yue Tsinghua University

Mostly Dark matter, Dark energy Composition of Universe Mostly Dark matter, Dark energy Known ~ 4% property of neutrinos not known very well 3

rotation velocity curve Direct detection of galactic dark matter WIMP Cs I Recoiled nucleus Recoil energy ~ 10’s keV Event rate < 1/kg/day Neutralinos the strongest WIMP candidate because they hardly interact and are stable Density of dark matter around the sun ~ 0.3 GeV /cm3 ( ~ 5 x 10-28 kg/cm3) 4

WIMP detection techniques Energy lost by recoiled nucleus converts to phonons, photons, ion pairs KIMS Phonon(heat) Photon(light) NaI(Tl), CsI(Tl), Xe W W Cryogenic detector Ge, Si + _ + _ + _ 2 phase Xe N Ionization HPGe detector

Yangyang Underground Laboratory(Y2L) 3.5 hours by car

Yangyang Underground Laboratory Korea Middleland Power Co. Yangyang Pumped Storage Power Plant Vertical Depth ~700m ~2 km KIMS

Detector and Shielding OFHC Cu 10cm : 3t

Why CsI(Tl)? Sensitive to both SD and SI WIMP interactions Ge, Xe not sensitive to SD proton coupling  complimentary to CDMS, XENON-10  direct check of DAMA signal by I-127 recoil Easy to get large mass with an affordable cost  annual modulation study High light yield ~60,000/MeV Pulse shape discrimination  better gamma rejection than NaI(Tl) Easy fabrication and handling

Detector CsI(Tl) Crystal 8x8x30 cm3 (8.7 kg) 3” PMT (9269QA) : Quartz window, RbCs photo cathode (Green enhanced) ~5 Photo-electron/keV Total charge spectrum for 59.5 keV Am241 Resolution @ 59.5 keV : 7.3%

Internal background Radioisotopes in the crystal 137Cs : 10 mBq/kg, 0.35 cpd/mBq/kg @ 10 keV 134Cs : 20 mBq/kg 0.07 cpd/mBq 0.005 cpd/mBq 87Rb : 10 ppb 1.07 cpd/ppb Geant Simulation Cs-137 reduction – use ultra pure water in powder prodcution; ~1.7 mBq/kg Rb reduction - recrystalization method ; < 1ppb Latest crystals are from ~2 cpd level powder 11

Other Detector Components Muon Detector 4 coverage muon detector : 28 channels Liquid Scintillator(5%) + Mineral Oil (95%) = 7 ton Measured Muon flux = 2.7 x 10 –7 /cm2/s Position resolution : σx, ~ 8 cm Reconstructed muon tracks with hit information Muon veto efficiency ~99.9% Neutron detector 1 ~ 1.2 liter BC501A liquid scintillator x 3 n/gamma separation using PSD E_vis > 300 keV Measured neutron flux (outside shield)  8 x 10 –7 /cm2/s ( 1.5 < E neutron < 6 MeV ) 12

Study of Muon induced neutrons Coincidence between Muon and Neutron detectors n/gamma separation using PSD Neutron energy: 0.4MeV<E<2.75MeV Measured : (3.8±0.7)10-2 counts/day/liter GEANT4 : (2.0±0.2) 10-2 counts/day/liter

Neutron calibration 300 mCi Am/Be source Tag γ(4.4MeV) to measure TOF and energy of neutrons 300 mCi Am/Be source  neutron rate 7 x 105 neutrons /sec  a few 100 neutrons/sec hit 3cm  3cm  3cm crystal ( sample )  Quenching factor of Recoil Energy NR mean time distribution Neutron sample Gamma Full size <t>=(S Ai ti)/S Ai Note: their shapes are Well matching 14

Data analysis for Wimp Search Data used for this analysis Crystal p.e./keV Mass(kg) Data(kg·days) S0501A 4.6 8.7 1147 S0501B 4.5 1030 B0510A 5.9 616 B0510B Total 34.8 3409

Data analysis for Wimp Search Calibration and control data samples Neutron ~ 500 kg days (at 4~6 keV) Gamma (using 137Cs) ~ 1100 kg days (0501A), 1650 kg days(0501B) 910 kg days (0510A), 840 kg days(0510B) PMT only ~350 kg days for each crystal with the PMTS used for each crystal clear box PMT 16

Reduction of PMT noise PMT noise log(τf) fit result for one event Decay time fit result for one event LL2-LL1 Gamma Neutron PMT only(dot-dashed) WIMP search DATA

Analysis Method: Event selection remove multi-crystal events 0.7 cpd bkg reduction 3-5 keV Asymmetry Cut Gamma PMT background WIMP search DATA 5-7 keV

Efficiency Compton events Neutron 19

WIMP search data with cut Event rates after cuts WIMP search data with cut S0501A S0501B B0510A B0510B Efficiency Corrected

NR event rate estimation Modeling of Calibration data with asymmetric gaussian function n g Electron recoil Nuclear recoil Best fit Fit the WIMP search DATA with PDF function from gamma and neutron calibration data  extract NR events rate 21

NR Event rates Extracted NR S0501A S0501B B0510A B0510B 22

Geant4 expectation 90% CL limit Total Rate: Extracted NR is fitted with simulated WIMP signal for each WIMP mass

is ruled out unambiguiously Cross-section upper limits Spin-Independent SD, Wimp-Proton PRL 99, 091301 (2007) ρD=0.3 GeV/c2/cm3 v0=220km/s, vesc=650km/s Systematic uncertainty ~15% Nuclear recoil of 127I of DAMA signal region is ruled out unambiguiously 24

2~4 cpd/keV/kg (preliminary) 12 crystal array Name Weight (kg) Data (kg days) S0406 6.7 237 S0501A 8.7 1147 S0501B 1030 B0510A 616 B0510B B0511 B0601 B0605A B0605B B0606A B0606B B0609 published PLB(2006) Pilot run published PRL(2007) Engineering run Total crystals 8.7 kg x 12 = 104.4 kg started data taking background level 2~4 cpd/keV/kg (preliminary)

Study of Muon Coincidence signal Muon coincidence event rate: ~6evt/hr for 12 detectors Muon coincidence event is very high energy event and triggers multi-crystals. It requires a few tens of ms for scintillation to disappear. High Energy muon event in CsI detector 5us (sec)

Muon Coincidence signal Event rate of muon tail event -> muon tail event is defined as the event which shows up within 30ms from the start of Muon coincidence event. Event rate of muon tail event for det0 20days data Multi hit event is rejected. 8ms dead time after high energy event is applied by hardware setting. cpd keV(electron recoil equivalent E)

Short remarks on Annual Modulation Study in KIMS Have been taking data with 100 kg array for ~7 months AM study without applying PSD can be done With 100kg CsI(Tl), ~3 cpd background level if no AM: one-year-run -> upper limit on AM amplitude < 0.01 cpd/keV/kg level with 90% CL if AM amplitude ~ 0.02 cpd/keV/kg two years data is required to confirm with more than 3σ significance 28

Summary and Prospects Result using 3409 kg days data PRL 99, 091301 (2007) DAMA signal region is ruled out for both SD and SI interactions at WIMP mass > 20 GeV Most stringent limit on SD interactions for pure proton case Successfully reduced internal backgrounds of CsI(Tl) crystals (latest powder ~ 2cpd) 12 full size crystals(8x8x30cm3) ~ 100 kg Current shielding can accomodate 250 kg 100 kg crystals installed in the shield and data taking was started  Annual modulation search 29

Elastic Sacttering of WIMP off a nuclues in the detector WIMP signal Elastic Sacttering of WIMP off a nuclues in the detector Very small 10-6 ~ 10-10 pb Expected event rate ~ 1/kg/day or less Very small Recoil energy < 100 keV Measured energy < 10 keV due to quenching R : event rate R0: total event rate E0: most probable incident kinematic energy r : kinematic factor, 4MwMN/(MW+MN)2 Very small

Analysis Method: Event selection Multi hit event rejection Fit quality cut fitted τf log likelihood value for two exponential fit and one exponential fit ratio of fitted mean time to the calculated mean time Short component rejection ratio of tail (t> 10 μs) to the whole amplitude Asymmetry cut

Effect of cuts on MT distribution Data Gamma Base cut Fit quality Asym tail PMT Neutron 34

Background level Previous run cpd preliminary keV PMT noise cut applied Muon tail events rejected Cut efficiency not corrected keV 36

Cross Section WIMP Nucleus Scattering Spin Independent Spin Dependent ρχ=galatic halo density vE=earth velocity in galatic frame v0=sun velocity in galatic frame Spin Independent Spin Dependent 37

WIMP Nucleus Cross section Latest WIMP search analysis results WIMP Nucleus Cross section Isotope J Abun <Sp> <Sn> 133Cs 7/2 100% -0.370 0.003 127I 5/2 0.309 0.075 73Ge 9/2 7.8% 0.03 0.38 129Xe 1/2 26% 0.028 0.359 131Xe 3/2 21% -0.009 -0.227 19F 0.441 -0.109 Scalar: Spin independent interaction -> coherent amplification via constituent nucleon Axial: Spin dependent interaction -> coupling depends on proton & neutron spin expectation value