Abstract
Very recently, the Xenon1T collaboration has reported an intriguing electron recoil excess, which may imply for light dark matter. In order to interpret this anomaly, we propose the atmospheric dark matter (ADM) from the inelastic collision of cosmic rays (CRs) with the atmosphere. Due to 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 $\sigma_e \sim {\cal O}(10^{-38}- 10^{-39}$) cm$^{2}$, and thus can evade other direct detection constraints. The search for light meson rare decays, such as $\eta \to \pi + \slashed E_T$, would provide a complementary probe of our ADM in the future.
Highlights
The existence of dark matter (DM) has been established in cosmological and astrophysical experiments
Because of the boost effect of high-energy cosmic rays (CRs), we show that the light atmospheric dark matter (ADM) can be fast moving and successfully fit the observed electron recoil spectrum through the ADM-electron scattering process
The very recent XENON1T electron recoil excess in the keV range may be the evidence of the light dark matter
Summary
The existence of dark matter (DM) has been established in cosmological and astrophysical experiments. The direct detections [1] that aim for weakly interacting massive particles (WIMPs) [2] have reached great sensitivities, which are approaching the irreducible neutrino floor Their null results produce very stringent limits on the WIMP DM-nucleus scattering cross section and lead to a shift of focus toward light dark matter particles [3,4]. When the DM particles scatter off these high-momentum electrons, the xenon atoms can be ionized in the liquid target In this process, the energy transfer to the detector is about ER ∼ keV. There are several astrophysical processes that can accelerate the dark matter to have velocities much higher than its galactic escape velocity [24,25,26,27] This kind of fastmoving dark matter will scatter with nucleus or electron of target in the direct detection and produce the detectable signals. To reconcile the tension between DM-nucleus and DM-electron scattering cross sections, we introduce a scalar mediator and a vector mediator, which couple with the quark and electron, respectively
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