Directly Detecting MeV-scale Dark Matter via Solar Reflection

TL;DR

This paper proposes a novel method to detect MeV-scale dark matter by leveraging solar reflection, which produces a higher-energy flux detectable by existing low-threshold detectors, leading to new constraints on dark matter interactions.

Contribution

It introduces the concept of solar reflection of light dark matter and provides the first detailed simulation and analysis of its detectability with current and future experiments.

Findings

Reflected dark matter flux is more energetic than ambient galactic DM.

Existing detectors can set new constraints on MeV-scale dark matter interactions.

Projected future experiments could improve sensitivity to low-mass dark matter.

Abstract

If dark matter (DM) particles are lighter than a few MeV/$c^2$ and can scatter off electrons, their interaction within the solar interior results in a considerable hardening of the spectrum of galactic dark matter received on Earth. For a large range of the mass vs. cross section parameter space, $\{m_e, \sigma_e\}$, the "reflected" component of the DM flux is far more energetic than the endpoint of the ambient galactic DM energy distribution, making it detectable with existing DM detectors sensitive to an energy deposition of $10-10^3$ eV. After numerically simulating the small reflected component of the DM flux, we calculate its subsequent signal due to scattering on detector electrons, deriving new constraints on $\sigma_e$ in the MeV and sub-MeV range using existing data from the XENON10/100, LUX, PandaX-II, and XENON1T experiments, as well as making projections for future low threshold direct detection experiments.