Dark Matter that Interacts with Baryons: Experimental Limits on the
  Interaction Cross-section for 27 Atomic Nuclei, and Resultant Constraints on
  the Particle Properties
  To constrain the properties of dark matter (DM) that interacts with nucleons,
we have conducted an experimental search for any anomalous heating of ordinary
baryonic matter at 77 K. Our tabletop experiment is motivated by the
possibility (discussed in a previous paper) that DM particles with masses in
the $\sim 1 - 2 m_{\rm p}$ range could be captured by and concentrated within
the Earth. For suitable parameters, this phenomenon could lead to a substantial
density $\sim 10^{14}\,\rm cm^{-3}$ of thermalized (300 K) DM particles at
Earth's surface that would heat cooler baryonic matter. Our experiment involves
precise differential measurements of the evaporation rate of liquid nitrogen in
a storage dewar within which various materials are immersed. The results
revealed no statistically-significant detections of heating in the 27 elements
with molar fractions $> 10^{-5}$ in Earth's crust. For material with the
average composition of Earth's crust, our measurements imply a $3 \sigma$ upper
limit of $1.32 \times 10^{-27}\, n_{\rm 14}^{-1} (m_{\rm DM}/2\,m_{\rm
p})^{-1/2}\,\rm cm^2$ on the mean cross-section for scattering with thermal
HIDM at 300 K, where $10^{14}\,n_{14} \, \rm cm^{-3}$ is the particle density
at Earth's surface. In combination with a lower limit on the scattering
cross-section, obtained from a consideration of the heat flow through the
Earth's crust (Neufeld, Farrar & McKee 2018), our experiment places an upper
limit of $1.6 \times 10^{13}\,\rm cm^{-3}$ on the density of DM at the Earth's
surface. This in turn, significantly constrains the properties for any DM
candidate that interacts with baryons.
