Prospects of Migdal Effect in the Explanation of XENON1T Electron Recoil Excess

TL;DR

This paper explores the potential of the Migdal effect to explain the electron recoil excess observed by XENON1T, proposing that low-energy nuclear recoils from dark matter interactions could account for the signal.

Contribution

It demonstrates that the Migdal effect can explain the XENON1T excess using GeV-scale neutron-philic dark matter with spin-dependent interactions, and considers boosted dark matter scenarios.

Findings

Migdal effect can reproduce the observed excess with GeV-scale dark matter.

Boosted MeV-scale dark matter can also induce detectable Migdal ionization.

The proposed explanation aligns with the energy range of the observed excess.

Abstract

The XENON1T experiment has recently announced the observation of an excess in electron recoil events at energy range of $1-7$ keV with a $3.5~\sigma$ signal significance over the Standard Model prediction. In this letter we sketch the prospects of explaining such an excess from Migdal ionization events with below threshold nuclear recoil energies. Interestingly, these are expected to show signal events in the ballpark energy scale of the observed excess. We demonstrate that the observed signal can be reproduced through the Migdal effect by an $\mathcal{O}(1)$ GeV neutron-philic dark matter having a spin-dependent coupling with the nucleus. A more optimistic scenario is explored where the Migdal ionization is driven by MeV scale boosted dark matter.