A Search for Dark Matter with NaI(Tl) Crystal of the KIMS-NaI

Abstract

A number of astrophysical observations provide evidences that the dominant matter in the universe is non-baryonic dark matter. Weakly interacting massive particles (WIMPs) are strong candidates of dark matter supported by many astronomical observations as well as theoretical predictions. Numerous direct searches of WIMP dark matter have been performed by using various detection techniques. KIMS-NaI experiment is working on the direct detection of WIMPs through weak interactions with nuclei in a NaI(Tl) crystal. KIMS-NaI collaboration installed the fi rst NaI(Tl) crystals in Yangyang underground laboratory in 2014 and crystal R&D and data taking are underway since then. The experiment uses pulse shape discrimination (PSD) between WIMP nuclear recoil signals and backgrounds for WIMP search. This thesis describes the PSD analysis study using NaI(Tl) crystal having high light yield. The measurements of the pulse shape produced by neutrons and gamma rays in a NaI(Tl) crystal are presented and the analyses of underground data from the fi rst two NaI(Tl) crystals based on this measurements are described. The understandings of the results from the PSD analysis are discussed and the preliminary limit using 667.16 kg days of data is described.