Dark Matter in the Earth II - When detectors turn blind
If the interaction strength becomes extremely strong another phenomenological aspect arises. Dark matter detectors are almost always located deep underground equipped with additional shielding layers of e.g. lead, to reduce background events such as atmospheric muons. For sufficiently strong interactions this overburden will also deflect and slow down incoming DM particles, and reduce the DM flux in the detector.
At some point we expect a decrease instead of an increase of the signal rate for higher cross sections, as visible in the first plot. Hence, the detector becomes insensitive to DM itself above a critical interaction strength, and direct detection experiments can only exclude a cross section interval for a given DM mass, as seen in the constraint plot. With the public DaMaSCUS-CRUST code, we can determine this critical cross section for any overburden or experiment using Monte Carlo simulations of DM trajectories in the shielding layers.