Constraints on GeV Dark Matter interaction with baryons, from a novel Dewar experiment

Dark matter which scatters off ordinary matter with a relatively large cross section cannot be constrained by deep underground WIMP experiments, due to the energy loss of DM along its path. However, for a sufficiently large cross section, DM particles in the GeV mass range can be captured and thermalized within Earth, resulting in the accumulation of a DM atmosphere whose number density can be as large as $10^{14} \text{ cm}^{-3}$ at Earth's surface. (If the DM-nucleon interaction is attractive and bound states can be formed, most DM bind to nuclei and the density is much lower.) Neufeld and Brach-Neufeld performed experiments to constrain the DM-baryon scattering cross section of DM atmosphere around Earth, by measuring the evaporation rate of liquid nitrogen in a storage dewar within which various materials are immersed. If the DM-nitrogen cross section is in an appropriate range, room temperature DM would penetrate the dewar walls and scatter on the cold nitrogen, increasing its evaporation rate beyond the observed level. Limits on the cross section of DM with other materials than nitrogen are obtained by adding known amounts of different materials; if the material is heated by interactions with DM, that heats and evaporates the liquid nitrogen. Because Born approximation is in general invalid in much of the relevant cross section regime, it is non-trivial to interpret such experimental results as a limit on the DM-nucleon cross section. In this paper we derive the constraints on DM-baryon scattering, with the interaction modeled as a Yukawa potential sourced by the finite sized nucleus. Combining the dewar constraints with BBN, we exclude for the first time a cross section above $10^{-26} \text{ cm}^{2}$ for DM mass 0.8-5.5 GeV, for any sign interaction. One DM model that is constrained is sexaquark $(uuddss)$ DM with mass $m_X \sim 2$ GeV; it remains viable.