We present a search for dark matter particles with sub-$\mathrm{GeV}/c^2$ masses whose interactions have final state electrons using the DarkSide-50 experiment’s $(12306\pm 184)\mathrm{kg}\mathrm{d}$ low-radioactivity liquid argon exposure. By analyzing the ionization signals, we exclude new parameter space for the dark matter-electron cross section ${\overline{\sigma }}_e$, the axioelectric coupling constant $g_{\mathrm{A}e}$, and the dark photon kinetic mixing parameter $\kappa$. We also set the first dark matter direct-detection constraints on the mixing angle ${|U_{e4}|}^2$ for $\mathrm{keV}/c^2$ sterile neutrinos.

• Received 28 July 2022
• Accepted 6 January 2023

DOI:https://doi.org/10.1103/PhysRevLett.130.101002

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Published by the American Physical Society