CsI crystal for WIMP Search

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CsI crystal for WIMP Search. For the KIMS Collaboration. Korea Invisible Mass Search. Seoul National Univ. : J.M.Choi, R.K.Jain, S.C.Kim, S.K.Kim*, T.Y.Kim, H.S.Lee, H.Park I.H.Park, E.Won, H.S.Won, H.Y.Yang, M.S.Yang - PowerPoint PPT Presentation

Transcript of CsI crystal for WIMP Search

  • CsI crystal for WIMP SearchSun Kee Kim Seoul National UniversityFor the KIMS Collaboration

    Seoul National Univ. : J.M.Choi, R.K.Jain, S.C.Kim, S.K.Kim*, T.Y.Kim, H.S.Lee, H.Park I.H.Park, E.Won, H.S.Won, H.Y.Yang, M.S.YangSejong Univ. : W.K.Kang, J.I. Lee, D.S.Lim, Y.D.Kim Yonsei Univ. : J.Hwang, H.J.Kim, J.H.Lee, Y.J.Kwon, Iwha Womans Univ. : I.S.Hahn, E.K.Lee SeongKyunKwan Univ. : I.S.Cho, D.H.Choi, S.H.Noh, I.Yu Chonbuk National Univ. : S.Y.Choi KAIST : P.Ko Univ. of Maryland : M.H.Lee, E.S.Seo, National Taiwan Univ., :H.B.Li, C.H.Tang, M.Z.Wang Academia Cinica :W.P.Lai, H.T. Wong , Inst. Of High Energy Physics : J.Li, Y.Liu, Q.Yue Inst. Of Atomic Energy : B.Xin, Z.Y.Zhou, Tsing Hua University : J.J.ZhuKorea Invisible Mass Search

  • Brief History of KIMS 1997 Summer : First discussion on WIMP search in Korea 1997 Fall : Started R&D on CsI(Tl) for WIMP search 1998 Summer : Demonstrated that CsI(Tl) can be used as a WIMP detector - presented at ICHEP98 1999 Spring : Started background measurement at Cheongphyung 2000 Summer : Project funded, KIMS collaboration formed 2001 August : TDR, Project Review Committee

  • CsI(Tl) Crystal CsI(Tl) NaI(Tl)Density(g/cm3) 4.53 3.67Decay Time(ns) ~1050 ~230Peak emission(nm) 550 415Hygroscopicity slight strongAdvantages High light yield ~50,000/MeV Pulse shape discrimination Easy fabrication and handling High mass number(both Cs and I)Disadvantages Emission spectra does not match with normal bialkali PMT => effectively reduce light yield 137Cs(t1/2 ~30y) ,134Cs(t1/2 ~2y) may be problematic

  • Photoelectron yieldFull size crystal (7x7x30) : ~ 4 p.e./keVSmall crystal(3x3x3) : 5~7 p.e./keVRbCs(green extended) PMT(D726UK)70% larger p.e. than the normal bialkali PMT

  • Neutron Beam TestKIGAM(Korea Institute of Geology and Material)3.2 MeV p : 3H(p,n)3He 2.62 MeV n

  • Quenching factorQF = Emeasured / Erecoilnn

  • Pulse Shape

  • Mean Time

  • Quality factorSBSBcutIdeal detector ~ 1, ~ 0K
  • CsI(Na) 1st measurement of CsI(Na)

  • ~ 2 hours from SNUPower plantHomyung Mt.()ReservoirLaboratoryAccess tunnel(1.4km)350mPukhan River()Underground Lab. at CheongpyungStorage Water Power Plant~1000 mwe

  • External background Cosmic rays : ~ 10-4 relative to the sea level Expected at ~400 m underground The rock composition : 238U ~ 4.8 ppm, 232Th ~ 6 ppm 40K ~ 4 ppm (ICP-Mass)

    Gamma background With a shielding of 15cm Pb + 10cm Cu(OFHC) Can be controlled < 0.005 cpd (counts/keV/kg/day) Neutron background Photonuclear interaction of cosmic ray muon Fission of 238U, (alpha,n) reaction With 30cm polyethylene + 20 cm Liquid scintillator Can be controlled

  • W/o shielding10cm Pb + 10 cm Cu(16 days data taking)100% HPGe installed in CPLGamma Background222Rn_up(226Ra)/222Rn_down(214PB,214Bi)=0.22+-0.06

  • Neutron Background~ 4x10-5 /cm2/secInput to the GEANT4 simulationMeasured with 0.5 liter BC501A liquid scintillator

  • Internal background137Cs : t 1/2= 30.07 year b decay to 137Ba* (Q = 1175.6 keV) 2 min life time, emitting 661.6 keV gamma Hard to reject => serious background at low energy134Cs : t 1/2 = 2.065 year b decsy to 134Ba* (Q=2058.7 keV) immediate gamma emission Can be rejected easily => not a serious problemRadioisotopes in the crystal - most important background after the proper shielding87Rb : t 1/2 half life = 4.75 x 1010 year (27.8% natural abundance) b Beta deacy to 87Sr (Q=282.3 keV) no gamma emission Hard to reject => potentially a serious problem => reduction technique in material is known

  • Internal background137Cs : ~155mBq/kg, 134Cs : ~35mBq/kg, 87Rb : 3.9 ppb0.63 cpd/1ppb 87Rb0.3 cpd/1mBq 137Cs0.005 cpd/1mBq 134Cs

  • 238U, 232Th in the crystal10~20 alphas/kg/day ~3 ppt (U+Th)

  • Measurement of Internal BackgroundCrystal 137Cs, 134Cs : direct measurement (fit to the MC prediction) Rb : direct measurement + chemical analysis U, Th : direct measurement of alphas ~ 15 ppt

    Powder 137Cs, 134Cs : 100% HPGe detector Rb : chemical analysis (ICP Mass)

    CsOH, CsNO3, Pollucite, Water 137Cs, 134Cs : 100% HPGe detector

  • Background measurement of powdersCrystalsCsMnO4~ 3mBq/kgCsI Powders137Cs ~14mBq/kgRb ~ 21 ppbCsOHCsNO3

    Chart3

    25.6

    14.220.9

    62.8

    9.71.7

    4.1200

    18.5

    13.5

    43.530.8

    106.6200

    83.2

    76.7

    3

    14.6

    9.4

    1553.94

    13.3203

    Chart1

    25.631.6

    14.222.8

    62.859.6

    9.79.7

    4.14.1

    18.529.8

    13.533.8

    43.538

    106.620.5

    83.251.2

    76.776.7

    33

    14.634.6

    9.416.1

  • 137Cs in Pollucite ?In CsI powder : 10~100 mBq/kg In Pollucite : < 5.8 mBq/kgProcessing water : 10.1 4.8 mBq/literExtraction of CsMnO4 from Pollucite with pure water 2.05 3.16 mBq/kg< 5.8 mBq/kg

  • CsI (30-50 keV) : 14.3 kg daysNaI(Tl) (35-40 keV) : 330 kg daysSurface effect ? V.A. Kudryavtsev et al., hep-ex/0109013

  • Shielding Design

  • Detector DesignCsI(Tl) 9cm x 9cm x 30cm ~ 11 kgPMT (3 inch RbCs)5x5 = 25 crystals ~ 275 kgQuartz20cm BC501A tagging efficiency > 75%

  • SensitivityAfter 1 year data takingwith 100 kg CsI(Tl) 2 keV threshold

  • Summary & Prospect Underground Lab. at CheongPyung is established Environmental background : low enough Comfortable place for long term experiment Extensive R&D on CsI(Tl) crystal has been carried out Low energy threshold ~ 2keV Pulse shape discrimination of -rays : promising Intrinsic background : almost understood Shielding design/Simulation/Electronics/DAQ Design almost at final stage Prospect ~100 kg CsI(Tl) crystal within this year 1 year data taking will cover DAMA region