Search for MeV Electron Recoils from Dark Matter in EXO-200

Abstract

We present a search for electron-recoil signatures from the charged-current absorption of fermionic dark matter using the EXO-200 detector. We report an average electron recoil background rate of $6.8\times 10^{-4}\mathrm{cts}{\mathrm{kg}}^{-1}{\mathrm{yr}}^{-1}{\mathrm{keV}}^{-1}$ above $4\mathrm{MeV}$ and find no statistically significant excess over our background projection. Using a total ${}^{136}\mathrm{Xe}$ exposure of $234.1\mathrm{kg}\mathrm{yr}$ we exclude new parameter space for the charged-current absorption cross-section for dark matter masses between $m_{\ddot{I}}‡=2.6\mathrm{MeV}-11.6\mathrm{MeV}$ with a minimum of $6\times 10^{-51}{\mathrm{cm}}^2$ at $8.3\mathrm{MeV}$ at the $90\%$ confidence level.

9 pages, 6 figures, 1 table