Dark matter, light mediators, and the neutrino floor

We analyze direct dark matter detection experiments for $\lesssim 100\mathrm{MeV}$ mass mediators with general interactions. We compare the nuclear recoil energy spectra from these interactions to the solar neutrino spectrum. A set of interactions that generate spectra similar to the neutrino background is identified; however, this set is distinct from those that mimic the neutrino background for $\gtrsim 100\mathrm{MeV}$ mass mediators. We outline a classification scheme based on momentum dependence of the dark matter–nucleus interaction to determine how strong the discovery limit for each interaction saturates due to the neutrino background. Our results motivate experimental progress towards lower nuclear recoil energy thresholds.

Figure 1

Best-fit recoil spectra fitted to ${}^8\mathrm{B}$ neutrino rates in germanium for ${\mathcal{O}}_1$ (left), ${\mathcal{O}}_{10}$ (middle), and ${\mathcal{O}}_6$ (right). The solid black line displays the spectrum for coherent neutrino scattering, while the other curves denote different mediator masses.

Figure 2

Discovery evolution of ${\mathcal{O}}_1$ (left), ${\mathcal{O}}_{10}$ (middle), and ${\mathcal{O}}_6$ (right). The curves show the limits for proton scattering only.