J. H. Choi

Limits on WIMP-nucleon cross section with CsI(Tl) crystal detectors

The Korea Invisible Mass Search(KIMS) experiment presents new limits on WIMP-nucleon cross section using the data from an exposure of 3409 kgd taken with low background CsI(Tl) crystals at Yangyang underground laboratory. The most stringent limit on the spin dependent interaction for pure proton case is obtained. The DAMA signal region for both spin independent and spin dependent interactions for the WIMP mass higher than 20 GeV/c^2are excluded by the single experiment with crystal scintillators.

New Limits on Interactions between Weakly Interacting Massive Particles and Nucleons Obtained with CsI(Tl) Crystal Detectors

The Korea Invisible Mass Search (KIMS) experiment presents new limits on the weakly interacting massive particle (WIMP)-nucleon cross section using data from an exposure of 3409 kg.d taken with low-background CsI(Tl) crystals at the Yangyang Underground Laboratory. The most stringent limit on the spin-dependent interaction for a pure proton case is obtained. The DAMA signal region for both spin-independent and spin-dependent interactions for the WIMP masses greater than 20 GeV/c2 is excluded by the single experiment with crystal scintillators.

First limit on WIMP cross section with low background CsI(Tℓ) crystal detector

Abstract The Korea Invisible Mass Search (KIMS) Collaboration has been carrying out WIMP search experiment with CsI ( T l ) crystal detectors at the YangYang Underground Laboratory. A successful reduction of the internal background of the crystal was done and a good pulse shape discrimination was achieved. We report the first result on WIMP search obtained with 237 kgu2009days data using one full-size CsI ( T l ) crystal of 6.6 kg mass.

AMoRE experiment: a search for neutrinoless double beta decay of 100Mo isotope with 40Ca100MoO4 cryogenic scintillation detector

AMoRE (Advanced Mo based Rare process Experiment) collaboration is going to use calcium molybdate crystals as cryogenic scintillation detector in a search for neutrinoless DBD of 100Mo isotope. Simultaneous detection of phonons and light will be used to reject internal background. A FWHM resolution of 0.2% in the phonon channel has been achieved with a 0.5 cm3 crystal. Several 40Ca100MoO4 crystals (≈ 0.5 kg) have been developed from enriched 100Mo and depleted 40Ca materials. The light yield of these crystals has been shown to be comparable with reference CaMoO4 scintillators for temperatures ranging down to 8 K. The content of dangerous radioisotopes in the crystals is under measurement. The projected sensitivity of the experiment for a 250 kg × years exposure is lim T1/2 ~ 3 × 1026 years, which corresponds to the effective Majorana neutrino mass mv ~ 0.02 – 0.06 eV.

Scintillation Properties and Internal Background Study of

Scintillation properties and radioactive contamination of calcium molybdate scintillating crystals depleted in ⁴⁸Ca and enriched in ¹⁰⁰Mo (⁴⁰Ca¹⁰⁰MoO₄ ) have been studied to prepare a ¹⁰⁰Mo-based neutrinoless double beta decay experiment. The prospects of a neutrinoless double beta decay experiment using ⁴⁰Ca¹⁰⁰MoO₄ crystals are discussed.

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The simultaneous measurement of heat and light signals from a 40Ca100MoO4 scintillating crystal was performed at temperatures of tens of milli-kelvin using a scintillating bolometric detector. The crystal was instrumented with a pair of low-temperature detectors, consisting of a metallic magnetic calorimeter for reading the phonon signals and a light detector based on a Ge light absorber, to simultaneously measure the scintillation light and phonon signals. This article presents the principle and performance, such as the event separation capability, of this simultaneous heat/light measurement system.

Ca

The response of CsI(Tl) crystals to nuclear recoils and gammas down to 3 keV has been studied, and it has been demonstrated that the pulse shape discrimination capability for CsI(Tl) is better than that for NaI(Tl). Extensive study of internal background of CsI powder was performed and a lot of efforts have been made to reduce the internal background sources such as 137Cs and 87Rb. The 137Cs concentration of 2 mBq/kg was achieved successfully in the CsI powder using ultra-pure water for whole extraction process. The Rb concentration was successfully reduced to be less than 1 ppb by the recrystallization method. The CsI(Tl) crystal used for the experiment was grown with the ultra-low background CsI powder and a dimension of the CsI(Tl) crystal is 8times8times30 cm3 which corresponds to weight of 8.7 kg. The number of photoelectrons is measured to be about 4-6/keV with a RbCs photocathode PMT. The background of CsI(Tl) crystals were measured in the shielding of 30 cm thick mineral oil, 15 cm thick lead, 5 cm thick polyethylene and 10 cm copper at the 700 m minimum depth of underground laboratory at YangYang Pumped Storage Power Plant in Korea. The WIMP search with low background CsI(Tl) crystals has been carried out by the Korean Invisible Mass Search (KIMS) Collaboration and the lower limit on WIMP-nucleon cross section are reported.

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A bstractThe results of a search for solar axions from the Korea Invisible Mass Search (KIMS) experiment at the Yangyang Underground Laboratory are presented. Low-energy electron-recoil events would be produced by conversion of solar axions into electrons via the axio-electric effect in CsI(Tl) crystals. Using data from an exposure of 34,596 kg · days, we set a 90 % confidence level upper limit on the axion-electron coupling, gae, of 1.39 × 10−11 for an axion mass less than 1 keV/c2. This limit is lower than the indirect solar neutrino bound, and fully excludes QCD axions heavier than 0.48 eV/c2 and 140.9 eV/c2 for the DFSZ and KSVZ models respectively.

MoO

We constructed a neutron calibration facility based on a 300-mCi Am-Be source in conjunction with a search for weakly interacting massive particle candidates for dark matter. The facility is used to study the response of CsI(Tl) crystals to nuclear recoils induced by neutrons from the Am-Be source and comparing them with the response to electron recoils produced by Compton scattering of 662-keV γ-rays from a 137Cs source. The measured results on pulse shape discrimination (PSD) between nuclear- and electron-recoil events are quantified in terms of quality factors. A comparison with our previous result from a neutron generator demonstrate the feasibility of performing calibrations of PSD measurements using neutrons from a Am-Be source.

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In order to understand the scintillation characteristics of nuclear recoil events in CsI(Tl) crystals and for application to the analysis of Dark Matter (DM) searches, we study quenching and channeling effects with simulations of recoil ion motion in CsI(Tl) and experiments using neutrons impinging on the crystal. The electronic energy loss versus penetration depth of recoil ions in a CsI(Tl) target are simulated by the SRIM and MARLOWE programs and modified by the application of a measured scintillation efficiency function. They are used to produce quenching factors as a function of recoil energy. The application of the MARLOWE code to a monocrystalline target yields a light yield distribution including tails which are correlated with ions enhanced ranges. The 2.4 MeV pulsed neutrons impinging on a monocrystalline CsI(Tl) target and an array of neutron detectors located at different scattering angles are used to measure the light yield distribution and the status of the measurement is reported.