Annual Modulation Study of Dark Matter Using CsI(Tl) Crystals In KIMS Experiment J.H. Choi (Seoul National University) SUSY2012, Beijing

SUSY Dark Matter Today’s Concordance Model of Universe -  CDM  K,0 = 1 – (  m,0 +  r,0 +  ,0 ) = 1 – (  b,0 +  cdm,0 +  ,0 + ,0 +  ,0 )  : Dark Energy : 73% CDM (Cold Dark Matter) : 23% Baryon : 4% Super Symmetry Theory WIMP(Weakly Interacting Massive Particle)

SUSY Milky Way Galaxy ~ 230km/s 2MASS The Milky Way has a large amount of dark matter halo The mass density of dark matter is about 0.3 GeV/cm 3 near the Sun The Milky Way rotates with the period of about 220 million years The sun revolves at the speed of about 230 km/s

SUSY Annual Modulation Annual Modulation of Velocity : ~ 6% arXiv: v1[astro-ph.CO]17Jan2011 < 3% 30km/s < 7%

SUSY Annual Modulation - KIMS Eur. Phys. J. C 67 (2010) 39 Spin Independent(WIMP-nucleon) Spin dependent (WIMP-proton ) DAMA reported the annual modulation amplitude of cpd/kg/keV (2~4keV) by the modulation fitting method KIMS reported the cross-section limit from the PSD(Pulse Shape Discrimination) method KIMS should see the same modulation if iodine is scattered by WIMP DAMAKIMS

SUSY Y2L Underground Laboratory Yangyang Underground Laboratory Depth : 700m (2000 mwe)

SUSY Detector Structure CsI Crystal Detectors - The 4x3 array of 12 CsI(Tl) crystals is installed in the innermost - Size of 8x8x30 cm, Mass of 8~9 kg(Total kg) - Each crystal is mounted with 2 PMTs on the both side Energy Resolution - 16~23%(FWHM) for keV Quenching Factor - CsI - Na : 30%, I : 9%, Ca : 8%, F : 12% CsI(Tl) crystal mounted PMTs Detector Shielding Moderator(Muon Det.) Lead shield Polyethylene Copper shield 12 x CsI(Tl) crystal

SUSY Electronics 400MHz FADC Electronics system digitize scintillation signals with 400MHz FADCs, which have a 10bit dynamic range and 40.96μs window Digitized signals are acquired by DAQ(Data AcQuisition) Program, which is working on ROOT based linux system DAQ rate is under 6Hz(0.5 million events/day) We are monitoring and managing the stability in real time with network and alarm systems (electric power, room temperature, crystal’s surface temperature, etc.) DAQ ProgramStabilities Signal

SUSY Data Taking Analysis is conducted with 30 month data from Sep to Feb DAQ time does not correspond to a full of month for each month because of a unavoidable problems, such as an outage of electricity or an abnormal termination of computers Total exposure is ton∙days with kg of CsI(Tl) crystals Sep ~ Feb. 2012

SUSY Noise & Background We are receiving 0.5 million events everyday The expected rate of WIMP signal is under 1 counts/kg/day considering DAMA Most of signals come from noise or background  Noise : electronics cables or circuits electronics noise PMT’s thermionic electrons from photocathode PMT’s afterpulses  Background : scintillation signals from particles Internal background ( 137 Cs, 134 Cs, 87 Rb, ……) External background ( 238 U, 232 Th, 40 K, ……) Cosmic background ( muon, ……) MC Simulation of Background

SUSY Event Selection Efficiency Multiple events survival probability after all the cuts are used to estimate the efficiency

SUSY Energy Spectrum (Single) Analysis was done by 11 detector except DET10 because of higher background rate X

SUSY Data Fitting A decay : Initial level ( 134 Cs) t 0 : Initial time – fixed to 1 Sep τ : Decay constant ( 134 Cs) – fixed to y Bkg : Constant background level A : Annual Modulation Amplitude ω : Period – fixed to 1 year t 1 : Annual Modulation Peak – fix to 2 Jun. Fitting Function DecayConstantModulation 2 Jun. X Parameter Correlation - χ 2 fitting A decay [cpd/kg/keV] Bkg [cpd/kg/keV] A decay [cpd/kg/keV] Bkg [cpd/kg/keV] Amplitude [cpd/kg/keV]

SUSY Averaged Result of 11 CsI(Tl) crystals A decay is typical beta spectrum of 134 Cs The background rate of 2 keV bin is relatively higher than other energy bin The amplitude of annual modulation corresponds to zero with 90% C.L. The averaged amplitude of annual modulation from 3 keV to 6 keV is ± cpd/kg/keV A decay Bkg Amplitude

SUSY KIMS & DAMA DAMA reported the annual modulation amplitude of ± cpd/kg/keV(8.3  ; 2~4 keV) 2~4 keV of DAMA corresponds to 3.24~5.41 keV of KIMS by 9% quenching factor of I The amplitude of annual modulation is ± cpd/kg/keV (1  ; 3~6 keV) in KIMS The 90% C.L. upper limit of amplitude of annual modulation is cpd/kg/keV (3~6 keV) in KIMS KIMS DAMA 3.24 keV5.41 keV

SUSY Conclusion  The analysis was done with 2.5 years data of ton  days using CsI(Tl) cryatals  The background level of single hit events is under 3 cpd/kg/keV passing 7 event selection conditions  The amplitude of annual modulation is consistent with zero by 90% C.L.  The amplitude of annual modulation is ± cpd/kg/keV (1  ) for 3-6 keV in KIMS experiment  The 90%CL upper limit is cpd/kg/keV(3-6 keV) in KIMS experiment, which is contradictory to the interpretation of WIMP-iodine scattering for DAMA modulation data

SUSY Thank You