E.J. Jeon

Understanding internal backgrounds in NaI(Tl) crystals toward a 200 kg array for the KIMS-NaI experiment

The Korea Invisible Mass Search (KIMS) collaboration has developed low-background NaI(Tl) crystals that are suitable for the direct detection of WIMP dark matter. Building on experience accumulated during the KIMS-CsI programs, the KIMS-NaI experiment will consist of a 200xa0kg NaI(Tl) crystal array surrounded by layers of shielding structures and will be operated at the Yangyang underground laboratory. The goal is to provide an unambiguous test of the DAMA/LIBRA annual modulation signature. Measurements of six prototype crystals show progress in the reduction of internal contamination from radioisotopes. Based on our understanding of these measurements, we expect to achieve a background level in the final detector configuration that is less than 1 count/day/keV/kg for recoil energies around 2xa0keV. The annual modulation sensitivity for the KIMS-NaI experiment shows that an unambiguous 7

Initial performance of the COSINE-100 experiment

sigma

Muon detector for the COSINE-100 experiment

σ test of the DAMA/LIBRA signature would be possible with a 600xa0kgxa0year exposure with this system.

Background model for the NaI(Tl) crystals in COSINE-100

We have developed ultra-low-background NaI(Tl) crystals to reproduce the DAMA results with the ultimate goal of achieving purity levels that are comparable to or better than those of the DAMA/LIBRA crystals. Even though the achieved background level does not approach that of DAMA/LIBRA, it is crucial to have a quantitative understanding of the backgrounds. We have studied background simulations toward a deeper understanding of the backgrounds and developed background models for a 9.16-kg NaI(Tl) crystal used in the test arrangement. In this paper we describe the contributions of background sources quantitatively by performing Geant4 Monte Carlo simulations that are fitted to the measured data to quantify the unknown fractions of the background compositions. In the fitted results, the overall simulated background spectrum well describes the measured data with a 9.16-kg NaI(Tl) crystal and shows that the background sources are dominated by surface

The COSINE-100 data acquisition system

^{210}

Dark Matter Search

210Pb and internal