Three-year annual modulation search with COSINE-100

Abstract

COSINE-100 is a direct detection dark matter experiment that aims to test DAMA/LIBRA's claim of dark matter discovery by searching for a dark-matter-induced annual modulation signal with NaI(Tl) detectors. We present new constraints on the annual modulation signal from a dataset with a 2.82 yr livetime utilizing an active mass of 61.3 kg for a total exposure of $173\text{ }\text{ }\mathrm{kg}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{yr}$. This new result features an improved event selection that allows for both lowering the energy threshold to 1 keV and a more precise time-dependent background model. In the 1--6 and 2--6 keV energy intervals, we observe best-fit values for the modulation amplitude of $0.0067\ifmmode\pm\else\textpm\fi{}0.0042$ and $0.0051\ifmmode\pm\else\textpm\fi{}0.0047\text{ }\text{ }\mathrm{counts}/(\mathrm{day}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{kg}\ifmmode\cdot\else\textperiodcentered\fi{}\mathrm{keV})$, respectively, with a phase fixed at 152.5 days.