Fig. 6: Emergence of plasmon in terms of Q with β and mV.
The dark matter–electron scattering cross section per atom, as a function of electron-hole pairs ionized, Q, following the ionization model from ref. 88 for various incoming particle speeds, β. The solid lines show the effect of including collective effects, i.e., using \({{{{\rm{Im}}}}}\left\{-\epsilon {(\omega ,k)}^{-1}\right\}\), as compared to excluding them (dash–dotted lines), i.e., using only \({{{{\rm{Im}}}}}\left\{\epsilon (\omega ,k)\right\}\). The collective effects screen the cross section at low Q. a shows the variation of the cross section with β; for high β ≳ 0.01, the plasmon becomes accessible and enhances the cross section. b shows the variation of the cross section with mV, where the plasmon excitation becomes apparent for mV ≲ 4 keV. These plots are made using the imaginary part of QCDark, where collective effects are modeled using Eq. (7).
