Muon and muon-induced phosphorescence events in the COSINE-100 Dark Matter Searches

Abstract

The COSINE-100 experiment is joint experiment by the KIMS-NaI~(Korean Invisible Mass Search) and the DM-Ice which aim to confirm or refute the annual modulation signal reported by DAMA/LIBRA using the same target material. In order to tag and suppress cosmic-ray muons, a muon detector was constructed using plastic scintillator panels that completely surround the crystal detector array at Yangyang Underground Laboratory (Y2L). High energy muons in the NaI(Tl) crystals and low energy scintillation signals corresponding to muon-induced phosphorescence events with half-lives longer than a few seconds were observed. The muon underground flux was measured to be 328 $\pm$ 1(stat.) $\pm$ 10(syst.) muons/$m^2$/day. In this report, a study of muon-induced phosphorescence events in the COSINE-100 are reported.