1. Annual Modulation Study of Dark Matter Using CsI(Tl) Crystals In KIMS Experiment J.H. Choi (Seoul National University) 2012. 8. 13. SUSY2012, Beijing

2. SUSY 2012 2 2012- 8-13 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)

3. SUSY 2012 3 2012- 8-13 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

4. SUSY 2012 4 2012- 8-13 Annual Modulation Annual Modulation of Velocity : ~ 6% arXiv:1101.5205v1[astro-ph.CO]17Jan2011 < 3% 30km/s < 7%

5. SUSY 2012 5 2012- 8-13 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 0.0183 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

6. SUSY 2012 6 2012- 8-13 Y2L Underground Laboratory Yangyang Underground Laboratory Depth : 700m (2000 mwe)

7. SUSY 2012 7 2012- 8-13 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 103.4 kg) - Each crystal is mounted with 2 PMTs on the both side Energy Resolution - 16~23%(FWHM) for 59.54 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

8. SUSY 2012 8 2012- 8-13 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

9. SUSY 2012 9 2012- 8-13 Data Taking Analysis is conducted with 30 month data from Sep. 2009 to Feb. 2012 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 75.53 ton∙days with 103.4 kg of CsI(Tl) crystals Sep. 2009 ~ Feb. 2012

10. SUSY 2012 1010 2012- 8-13 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

11. SUSY 2012 1 2012- 8-13 Event Selection Efficiency Multiple events survival probability after all the cuts are used to estimate the efficiency

12. SUSY 2012 1212 2012- 8-13 Energy Spectrum (Single) Analysis was done by 11 detector except DET10 because of higher background rate X

13. SUSY 2012 1313 2012- 8-13 Data Fitting A decay : Initial level ( 134 Cs) t 0 : Initial time – fixed to 1 Sep. 2009 τ : Decay constant ( 134 Cs) – fixed to 2.065 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]

14. SUSY 2012 1414 2012- 8-13 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 0.0008±0.0068 cpd/kg/keV A decay Bkg Amplitude

15. SUSY 2012 1515 2012- 8-13 KIMS & DAMA DAMA reported the annual modulation amplitude of 0.0183±0.0022 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 0.0008±0.0068 cpd/kg/keV (1  ; 3~6 keV) in KIMS The 90% C.L. upper limit of amplitude of annual modulation is 0.0119 cpd/kg/keV (3~6 keV) in KIMS KIMS DAMA 3.24 keV5.41 keV

16. SUSY 2012 1616 2012- 8-13 Conclusion  The analysis was done with 2.5 years data of 75.53 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 0.0008±0.0068 cpd/kg/keV (1  ) for 3-6 keV in KIMS experiment  The 90%CL upper limit is 0.0119cpd/kg/keV(3-6 keV) in KIMS experiment, which is contradictory to the interpretation of WIMP-iodine scattering for DAMA modulation data

17. SUSY 2012 1717 2012- 8-13 Thank You