Research Program and Status of KIMS Sun Kee Kim Seoul National University Yongpyung, Jan. 29, 2004

Status and issues in particle physics SM is satisfactory but not complete Explain experimental data Too many parameters Origin of mass unknown Beyond Standard Model String Supersymmetry Unification Extra Dimension Connection to cosmos Higgs paricle CP violation Mass of neutrino Identification of DM New Experimental Data Needed New accelerator LHC/LC B-factory, Tevatron Neutrino experiment Double beta decay WIMP search *hints : neutrino oscillation, many evidence of dark matter precision measurement of CP violation

KIMS CsI(Tl) crystal WIMP search at Yanyang Underground Laboratory H.C.Bhang, S.C.Kim, S.K.Kim, S.Y.Kim, J.W.Kwak, H.S.Lee S.E.Lee, J. Lee, S.S.Myung, H.Y.Yang Seoul National University Y.D.Kim, J.I. Lee, D.S.Lim Sejong University M.J.Hwang, H.J.Kim, Y.J.Kwon Yonsei University I.S.Hahn, E.K.Lee, I.H.Park Ewha Womans University M.H.Lee, E.S.Seo Univ. of Maryland J.Li Institute of High Energy Physics J.J.Zhu Tsinghua University Korea Invisible Mass Search

Research Program of KIMS Dark matter search CsI(Tl) crystal detector  H.S.Lee’s talk Cryogenic detector  S.C.Kim’s talk Other new detector R&D : Xe, Ar,… Double beta decay search Metal loaded liquid scintillator Crystals : CaMoO4, GSO,…  H.J.Kim, D.S.Lim, M.J.Hwang’s talk Other activities Artificial neutrino source  Y.D.Kim’s talk HPGe detector – low level radioactovoty measurement  E.K.Lee’s talk

Mostly Dark matter, Dark energy CMB measurement Composition of Universe Farthest Supernovae Nucleosynthesis Abundance of light elements Visible starts

WIMP Certain classes of SUSY model predict Neutralino as LSP : stable weak interaction scale annihilation cross section proper relic density for dark matter Neutralino : super-partners of neutral gauge bosons, higgs  Excellent CDM candidate         f f f f f f W+W+ W-W- Z H,h f ++

Elastic Sacttering of WIMP off a nuclues in the detector ~ pb Expected event rate ~ 1/kg/day or less WIMP signal R : event rate R 0 : total event rate E 0 : most probable incident kinematic energy r : kinematic factor, 4M w M N /(M W +M N ) 2 Recoil energy < 100 keV Measured energy < 10 keV due to quenching

Annual Modulation v sun =232km/s sun earth v orbit =30km/s =60 o v earth =v sun +v orbit coscos[(t-t o )] =2/T : T=1year t o = June 2 S=S o +S m cos[(t-t o )] S m /S o ~ 0.05 ~5% t June December S Need large mass

~100 kg NaI(Tl) crystals kg days DAMA vs Others

100kg 10 cpd 100kg 1 cpd 100kg 0.1cpd 1t 0.1 cpd KIMS Sensitivity

Issues in CsI WIMP search Reduction of internal background : purification of CsI powder Reduction/monitoring of external background  Underground laboratory  Shielding  Muon veto and tagging (J.J.Zhu’s talk)  Neutron flux monitoring (J.W.Kwak’s talk)  Radon monitoring (M.J.Lee’s talk) Calibration of PSD (J.Lee’s talk) Simulation (S.S.Myung’s talk) Electronics & DAQ (S.Y.Kim’s talk) Taking data  has been taking data with one crystal smoothly

Purification of CsI powder Reduction of 137 Cs Cause : water is polluted with 137 Cs Solution : Use purified water in all the process of Cs extraction from the pollucite  First try with relatively pure water : successful ~ 5 mBq/kg  Consistent with 137 Cs contamination in the used water Need further purification of water (10 18 Mohm)  Companies(Chemetall and Wuhan) agreed to carry out this R&D  < 1mBq/kg looks possible Reduction of Rb Cause : originally in the pollcite and chemically similar to Cs Solution : Re-crystallization  Re-crystallization of the powder can be repeated as needed  Proved to reduce the Rb contamination < 1ppb achieved

Summary of Internal Background Reduction Powder production with higher purity water will be done in 2004  expect below 1 cpd

Reduction of Internal Background When we started Now New crystal In production Study of the internal background of CsI(Tl) crystal detector for dark matter search Nucl. Instrum. Meth. A. (2003) Measurements of Cesium Radioisotopes in Cesium Compound, J. Kor. Phys. Soc.(2002)

External Background Neutron background : generate nuclear recoil  identical to the WIMP signal Sources of neutrons : (alpha,n) reaction, alphas from radioactive decays in rocks cosmic ray muon interaction Neutrons from rocks can be avoided by a proper shielding But, if muons interact within the shield, neutrons can enter the detector  Need to reduce the muon flux as much as possible  Deep underground experimental site Gamma background : can be prevented by proper shielding

Cheongpyung Yangyang Lab. SNU International Airport Seoul 3.5hours by car 襄陽 We are here

Yangyang Underground Laboratory Korea Middleland Power Co. Yangyang Pumped Water Power Plant Yangyang Underground Laboratory Minimum depth : 700 m / Access to the lab by car (~2km) Completion of the power plant(2006)  large space available Construction of the laboratory buildings done

Shielding design GEANT-4 simulation was used Gammas coming from decays of 238 U chain, 232 Th chain, 40 K in the surrounding rocks and concrete : 15cm thick Pb + 10 cm Cu Neutrons external neutrons : 30 cm mineral oil + 5 cm polyethylene muon induced : veto by muon detector + monitoring by neutron detector inside the lead shield 222 Rn in the air : flowing N2 gas inside the copper shield monitoring by Rn detector << 0.01 cpd/kg/keV

Mineral oil 30cm Boliden Lead 15cm : 30t OFHC Cu 10cm : 3t Radon detector  M.J.Lee’s talk Muon detector  J.J.Zhu’s talk Neutron detector  J.W.Kwak’s talk Shielding and background detctors 2~4 pCi/liter

FADC Performance

SUMMARY Established an underground laboratory(700 m deep) at Yanyang Extensive R&D on CsI(Tl) crystal done Shielding structure and other detectors in operation  Data taking for long term has done smoothly R&D on various underground experiments is on going Phase I WIMP search : 100 kg starting in 2004