Novel Search for absorption of ultra-light fermionic dark matter on electron with cosmic ray boost

Abstract

The search for the absorption of fermionic dark matter (DM) on electron is hindered by a partial or complete loss of sensitivity for the mass of DM ($m_{\ddot{I}}‡$) below $\mathcal{O}(10)$ keV. We introduce a novel search using a small but high-energy portion of DM boosted by cosmic rays, and the loss of sensitivity is circumvented because the subsequent absorption within the detector imparts to the target electron not only $m_{\ddot{I}}‡$ but also substantial $T_{\ddot{I}}‡$. The one-sided 90\% confidence level constraints on ($\ddot{I}{ƒ}_e{v}_{\ddot{I}}‡$) are derived with the XENONnT public dataset for $m_{\ddot{I}}‡$ $\in$ (1$\times$10${}^{-5}$--1) keV which has not been explored yet. Our results have placed constraints on DM at the lowest $m_{\ddot{I}}‡$ currently achievable among the DMDD experiments utilizing ionizing signals from DM interactions within the detectors.