MeV-scale dark matter deep underground

We demonstrate that current and planned underground neutrino experiments could offer a powerful probe of few-MeV dark matter when combined with a nearby high-intensity low-to-medium energy electron accelerator. This experimental setup, an underground beam-dump experiment, is capable of decisively testing the thermal freeze-out mechanism for several natural dark matter scenarios in this mass range. We present the sensitivity reach in terms of the mass-coupling parameter space of existing and planned detectors, such as Super-K and SNO+, in conjunction with a hypothetical 100-MeV energy accelerator. This setup can also greatly extend the sensitivity of direct searches for new light weakly coupled force carriers independent of their connection to dark matter.