Constraints on low-mass, relic dark matter candidates from a surface-operated SuperCDMS single-charge sensitive detector

This article presents an analysis and the resulting limits on light dark matter inelastically scattering off of electrons, and on dark photon and axionlike particle absorption, using a second-generation SuperCDMS high-voltage eV-resolution detector. The 0.93 g Si detector achieved a 3 eV phonon energy resolution; for a detector bias of 100 V, this corresponds to a charge resolution of 3% of a single electron-hole pair. The energy spectrum is reported from a blind analysis with 1.2 g-days of exposure acquired in an above-ground laboratory. With charge carrier trapping and impact ionization effects incorporated into the dark matter signal models, the dark matter-electron cross section ${\overline{\ensuremath{\sigma}}}_{e}$ is constrained for dark matter masses from 0.5 to ${10}^{4}\text{ }\text{ }\mathrm{MeV}/{c}^{2}$; in the mass range from 1.2 to $50\text{ }\text{ }\mathrm{eV}/{c}^{2}$ the dark photon kinetic mixing parameter $ϵ$ and the axioelectric coupling constant ${g}_{ae}$ are constrained. The minimum 90% confidence-level upper limits within the above-mentioned mass ranges are ${\overline{\ensuremath{\sigma}}}_{e}=8.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}34}\text{ }\text{ }{\mathrm{cm}}^{2}$, $ϵ=3.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$, and ${g}_{ae}=1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$.