Figure 1

Left panel: Ratio of the differential rate of recoil events induced by bound DM over the one induced by ordinary halo DM as a function of $m_{\chi }$ at recoil energy 1 eV. This ultralow recoil energy is chosen for illustrative purposes: At 1 eV, all elements in the Earth contribute to the bound DM signal. We consider a germanium detector with perfect energy resolution and three dark matter-nucleon interaction types with differential cross sections scaling as reported in the legend. Thin colored lines assume capture by single elements in the Earth and a differential cross section $\propto 1/v^2$. For this interaction type, we also consider the ratio of directional rates. Note that the ratio for $q^2/v^2$ interactions must be rescaled by a factor of $10^3$. Central panel: Same as for the left panel for a recoil energy of 20 eV. Right panel: Arbitrarily normalized differential rates of recoil events as a function of the recoil energy for a DM particle mass of 50 GeV. Solid lines correspond to total rates, while dashed lines to the associated halo DM particle contribution. Vertical lines show the threshold energies of selected present and projected experiments (for reference, we also include DAMIC, though it uses silicon as target material).