Search for low-mass dark matter with CsI(Tl) crystal detectors

We present a search for low-mass (≤20 GeV/c²) weakly interacting massive particles (WIMPs), strong candidates of dark matter particles, using the low-background CsI(Tl) detector array of the Korea Invisible Mass Search experiment. With a total data exposure of 24,524.3 kg days, we search for WIMP interaction signals produced by nuclei recoiling from WIMP-nuclear elastic scattering with visible energies between 2 and 4 keVee (electron-equivalent energy). The observed energy distribution of candidate events is consistent with null signals, and upper limits of the WIMP-proton spin-independent interaction are set with a 90% confidence level. The observed limit covers most of the low-mass region of parameter space favored by the DAMA annual modulation signal assuming the standard halo model.