On-shell mediator dark matter models and the Xenon1T anomaly

TL;DR

This paper proposes a dark matter model involving on-shell mediators to explain the Xenon1T electron recoil excess, fitting the energy spectrum and consistent with astrophysical and underground detection constraints.

Contribution

It introduces a novel on-shell mediator dark matter model that accounts for the Xenon1T anomaly with a specific decay chain and velocity distribution of the final state particle.

Findings

The model fits the Xenon1T electron recoil spectrum.

The predicted flux of the final state particle is consistent with astrophysical observations.

The interaction cross section allows particles to reach underground detectors.

Abstract

We present a dark matter model to explain the excess events in the electron recoil data recently reported by the Xenon1T experiment. In our model, dark matter $\chi$ annihilates into a pair of on-shell particles $\phi$ which subsequently decay into $\psi \psi$ final state; $\psi$ interacts with electron to generate the observed excess events. Due to the mass hierarchy, the velocity of $\psi$ can be rather large and can have an extended distribution, which provides a good fit to the electron recoil energy spectrum. We estimated the flux of $\psi$ from dark matter annihilations in the galaxy and further determined the interaction cross section which is sizable but small enough to allow $\psi$ to penetrate the rocks to reach the underground labs.