Neutrinos as background and signal in searches using the Migdal effect

TL;DR

This paper investigates how neutrino backgrounds affect dark matter searches using the Migdal effect, mapping the neutrino fog and emphasizing the importance of neutrino-induced signals in detection strategies.

Contribution

It quantifies the neutrino fog in Migdal effect-based dark matter detection and highlights the significance of neutrino-induced processes for semiconductor and noble liquid targets.

Findings

Neutrino backgrounds create a neutrino fog in dark matter parameter space.

Inclusion of neutrino-induced Migdal effects is crucial for accurate detection modeling.

Large parts of the relic density parameter space are within the neutrino fog.

Abstract

Ionization or excitation resulting from the noninstantaneous response of the electron cloud to nuclear recoil is known as the Migdal effect. Dark matter searches utilizing this process set the most stringent bounds on the spin-independent dark matter-nucleon scattering cross section over a large region of the sub-GeV dark matter parameter space, underscoring its significance in dark matter detection. In this paper, we quantify the regions of dark matter parameter space that are challenging to probe via the Migdal effect due to the presence of dominant solar neutrino backgrounds for both liquid noble and semiconductor targets. Our findings reveal that there is no hard floor in the dark matter parameter space. Instead, we map the so-called neutrino fog. In mapping the neutrino fog, we identify the importance of incorporating the Migdal effect induced by neutrinos, as well as neutrino-electron scattering and dominant coherent neutrino-nucleus scattering, particularly for semiconductor targets. Furthermore, we demonstrate that a large portion of the relic density allowed parameter space lies within the neutrino fog. Finally, we estimate the exposure required to detect neutrino-induced Migdal events in direct detection experiments.