Status of KIMS Sun Kee Kim Seoul National University For the KIMS Collaboration Workshop on Undeground Experiments and Astroparticle Physics Feb. 16, 2005

KIMS H.C.Bhang, J.H.Choi, S.C.Kim, S.K.Kim, S.Y.Kim, J.W.Kwak, J.H.Lee H.S.Lee, S.E.Lee, J. Lee, S.S.Myung, H.Y.Yang Seoul National University Y.D.Kim, J.I. Lee Sejong University H.J.Kim Kyungpook National University M.J.Hwang, Y.J.Kwon Yonsei University I.S.Hahn, 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, D. He, Q.Yue Tsinghua University Korea Invisible Mass Search

Research Program of KIMS WIMP Search - CsI(Tl) crystal detector running  1 st result is reported - Ultra-low background HPGe detector in preparation for R&D setup - Development of cryogenic detector R&D effort is on going Neutrinoless double beta decay Search - Metal loaded liquid scintillator pilot experiment is running – a preliminary result - CaMoO 4 crystal R&D effort is on going

WIMP Search Signature : WIMP-nucleus elastic scattering  Signal by recoiled nucleus Background : gammas from radioactive isotopes inside/outside detector  partially or fully distinguishable from WIMP signal neutrons : indistinguishable from WIMP signal neutrons from alpha-n reaction : can be stopped by shield neutrons from muon photo-production : difficult to stop  need to go underground

Gaitskell’s summary talk IDM2004

DAMA vs. CDMS

They evaluated SD limit of CDMS with small natural abundance of spin odd isotopes in silicon (4.68% Si-29) and germanium (7.73% Ge-73) DAMA result survives m_wimp<~20GeV

If the ratio of the two nucleon matrix element to the atomic number varies from one nucleus to the next, so will the degree of the cancellation. Thus, when the two-nucleon contribution is taken into account, a dark-matter candidate that appears in the DAMA collaboration but not in other searches [14] is conceivable for a WIMP with SI interactions even within the framework of the MSSM. In conclusion, we have shown that the two-nucleon and one-nucleon currents can give comparable contributions to the WIMP-nucleus scattering and point out that this result can help resolve the conflict between the various direct dark-matter search experiments.

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

Environment Parameters DepthMinimum 700 m Temperature20 ~ 25 o C Humidity35 ~ 60 % Rock contents 238 U less than 0.5 ppm 232 Th 5.6 +/- 2.6 ppm K 2 O 4.1 % Muon flux 4.4 x /cm 2 /s Neutron flux 8 x /cm 2 /s 222 Rn in air 2 ~ 4 pCi/liter Temperature stability of CsI(T l ) crystal detector /- 0.2 o C N 2 flowing rate = 4 liter / min For Rn Reduction and low humidity

KIMS Neutron shield / Muon det. Lead shield Polyethylene Copper shield CsI(Tl) crystal

Muon Detector 4  coverage muon detector : 28 channels Liquid Scintillator(5%) + Mineral Oil (95%) = 7 ton Measured Muon flux = 4.4 x 10 – 7 /cm 2 /s Position resolution :  x, ~ 8 cm Reconstructed muon tracks with hit information

1liter BC501A liquid scintillator n/g separation using PSD E_vis > 300 keV Neutron Monitoring Detector 214 Bi -decay  214 Po -decay

Neutron Monitoring Detector(cont’d) 222 Rn -decay  218 Po -decay 230 Ra dominant contamination in 238 U chain cnts/liter/day – 1.5 x10 -6 ppt of 230 Ra level 232 Th dominant contamination in 232 Th chain cnts/liter/day ppt of 232 Th level All neutron candidate events are consistent with alphas from internal sources Neutron rate < 1.8 cpd (90 % confidence level ) inside the shield * Neutron rate outside the shield= 8 x 10 –7 /cm 2 /s ( 1.5 < E neutron < 6 MeV ) After subtracting internal background estimated from the data inside the shield

Neutrons induced by muons Log 10 (t) Energy [MeV] Neutron region Energy [MeV] Two strong candidates of neutron induced by muon  2 events for days  cnts/liter/day Coincidence between muon and neutron detector

Radon Monitoring Detector Electrostatic alpha spectroscopy : 70 liter stainless container Use Si(Li) photodiode : 30 x 30 mm Estimate 222 Rn amount with energy spectrum of a from 218 Po & 214 Po. Photodiode calibration : 210 Po, 241 Am 222 Rn in air = 1 ~ 4 pCi/liter Absolute efficiency calibration done with 226 Ra

KIMS DAQ system Blue part : Home made Yellow part : commercial Root based DAQ on linux 500MS/s DIGITIZER

Neutron calibration facility in SNU 300 mCi Am/Be source  neutron rate 7 x 10 5 neutrons /sec  a few 100 neutrons/sec hit 3cmX3cm crystal  Quenching factor of Recoil Energy Take Neutron calibration data PSD check – Quality factor 46 o CsI BC501a LSC 90 o 17.4 o n Am/Be Tag γ(4.4MeV) to measure TOF and energy of = 10 keV 137 Cs Compton Neutron Recoil Background data

Internal background of CsI Crystal 137 Cs (artificial) –serious background at low energy 134 Cs (artificial+ 133 Cs(n,gamma)) 87 Rb (natural) –Hard to reject  reduction technique in material is known Single Crystal (~10 kg) ~10keV 87 Rb 1.07 cpd/1ppb 137 Cs 0.35 cpd/1mBq/kg 134 Cs 0.07 cpd/1mBq/kg 137 Cs : 10 mBq/kg 134 Cs : 20 mBq/kg 87 Rb : 10 ppb 87 Rb 137 Cs 134 Cs keV CPD Geant Simulation

Reduction of Internal Background Best available Crystal at Market 70cpd Powder Selection 20cpd Cs137 Reduction Using Pure water 14cpd Rb87 Reduction by Re- crystallization 6cpd

2mBq/kg  0.7 cpd/keV/kg Further reduction of internal background ? New CsI powder produced with ultra pure water

CsI Data Taking  Data for WIMP search  430 kg days for 8x8x30 cm 3 crystal of 14 cpd background level 2004 spring  237 kg days for 8x8x23 cm 3 crystal of 6 cpd background level 2004 summer  CsI(Tl) Crystal 8x8x30 cm 3 (8.7 kg) : 16 cpd 8x8x23 cm 3 (6.6 kg) : 6 cpd  3” PMT (9269QA) Quartz window, RbCs photo cathode  DAQ 500MHz FADC

Latest Arrival ! Two crystals of 6cpd background Taking data with total 3 crystals ~20kg.

Log Mean Time distribution of Neutron & 137 Cs Compton & Data 3~4 keV4 ~5 keV 11~12 keV 10~11 keV9~10 keV 8~9 keV7~8 keV 6~7 keV 5~6 keV Preliminary

Extraction of nuclear recoil signals WIMP mass 20 GeV/c 2 60 GeV/c GeV/c GeV/c 2 Preliminary

Preliminary Limit curve  Dark matter density at the solar system   D = 0.3 GeV c -2 cm -3  Use annual average parameters V 0 = 220 km s -1, V E = 232 km s -1, V Esc = 650 km s -1 Preliminary

Search for low mass WIMP Limited by threshold ULE HPGe detector Collaboration with China and Taiwan

Status of ULE HPGe detector setup CsI(Tl) crystal Compton veto  Built by TU  Delivered to SNU 5g 1 cpd level detector Tested at Academia Cinica, Taiwan To be delivered to SNU in Dec. If successful  upgrade to 1kg mass

R&D on cryogenic diamond detector Diamond absorber: By the Debye T 3 law, specific heat ~k B (T/) 3, : Debye Temperature Superconducting film: Mo(50nm), Cu(200nm) length: 3mm, width: 0.1mm Mass of Cu : 5.376e-7g, Mass of Mo: 1.53e-7g Heat capacity: 8.99e-13 J/K cryostat absorbe r R s ~m  ~V~V ~k  TES ~  Squid Cryogenic detector operating at ~100mK can  detect very energy deposition by phonon measurement  separate electron recoil from nuclear recoil by simultaneous measurement of ionization R Bias point TTcTc

R(  ) T(K) T c ~ 0.4 Mo electrode Mo/Cu bilayer(3x0.1mm) Development of TES sensor and test Several samples of TES on Sil wafer  RT curve was measured using an adiabatic demagnetization refrigerator

Double beta decay search program Calorimetric approach source = detector Metal loaded liquid scintillator Sn, Nd, Zr organic compounds into the base scintillator (PC 1 liter + PPO 4 g + POPOP 15 mg) Crystal scintillator CaMoO 4 Strong indication of non-zero neutrino mass by neutrino oscillation Nature and absolute mass of neutrino can be explored by 0νββ decay

Neutrino oscillation :  at least one neutrino has mass ~ 50meV Heidelberg-Moscow experiment : positive evidence(?) ~ 400 meV

Tin loaded Liquid Scintillator Dimension R = 5cm H = 15.2cm V = 1.18L TMSN50% by CAMAC -> 123 days T 1/2 = 5.56x10 19 year by 90% C.L TMSN50% by 500MHz FADC -> 33 days T 1/2 = 3.41x10 19 year by 90% C.L pol3 + gaus fitting E e (keV) Tetramethyle Tin(50%) + LS LS made of * Solvent ; PC 1L * Solute ; POP 4g * Second-solute ; POPOP 15mg * World best limit(Sn-124) = 2.4x10 17 year (1952) 2287keV

CaMoO 4 S.B. Mikhrin et.al, NIMA 486 (2002) 295 Light yield : 20% of CsI(Tl) Peak wave length : ~ 520 nm Decay time : ~ 16 μs Light increase with lower temperature Measurement done by ITEP & Minsk 1.8x1.8x3.5 cm 3 In collaboration with Russian group

Sensitivity 10kg ( 100 Mo) 0.01 /kg/keV/y 6% FWHM resolution 5year  7.7x10 24 y(~200 meV) Current best limit on 100Mo : 3.5x10 23 by NEMO3 with 6.9kg 100 Mo Claim by Klapdor-Kleingrothaus et al.  ~ 400 meV Test result and Prospect Np.e. ~400/MeV Alpaha/Gamma separation R&D in progress -Crystal growing optimization  increasing light yield by factor 3-4 -Temperature dependence -Reduction of internal background -100Mo enrichment (9.8%  95%)

Summary and prospects – WIMP search with CsI(Tl) crystal All the detectors and shielding in operation as designed at 700 m deep underground laboratory at Yangyang Reduction of internal background of CsI successful  Expect ~ 1cpd crystal First limit on WIMP cross section with 6.6kg 6cpd crystal  Already competitive to other crystal detectors  Two more crystals ~20kg taking data now  With larger mass and (even) lower background crystals we can reject(confirm) DAMA result in a year !

Summary and prospect –other activities ULE HPGe detector for low mass WIMP search  Compton veto detector delivered  Prototype detector and shield will be installed soon Cryogenic detector for low energy detection  Fabrication and test of TES sensor on-going  Need fast cycling of sample test for the TES optimization Metal loaded liquid scintillator for 0  decay  Pilot experiment with 1 liter 50% Sn loaded LS  encouraging result  Study on internal background in progress  Loading other element in progress CaMoO 4  Test with a 50g crystal has been done  encouraging resut  R&D for growing optimization and background reduction in progress