Very recently, the XENON1T Collaboration has reported an intriguing electron recoil excess, which may imply light dark matter. To interpret this anomaly, we propose the atmospheric dark matter (ADM) from the inelastic collision of cosmic rays (CRs) with the atmosphere. Because of the boost effect of high-energy CRs, we show that the light ADM can be fast moving and successfully fit the observed electron recoil spectrum through the ADM-electron scattering process. Meanwhile, our ADM predicts the scattering cross section ${\sigma }_e\sim \mathcal{O}({10}^{-38}-{10}^{-39}{\mathrm{cm}}^2$) and thus can evade other direct detection constraints. The search for light meson rare decays, such as $\eta \to \pi +{\cancel{E}}_T$, would provide a complementary probe of our ADM in the future.

• Received 11 July 2020
• Accepted 25 November 2020

DOI:https://doi.org/10.1103/PhysRevD.102.115028

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Published by the American Physical Society