We present improved germanium-based constraints on sub-GeV dark matter via dark matter–electron ($\chi \text{−}e$) scattering using the $205.4\mathrm{kg}·\mathrm{day}$ dataset from the CDEX-10 experiment. Using a novel calculation technique, we attain predicted $\chi \text{−}e$ scattering spectra observable in high-purity germanium detectors. In the heavy mediator scenario, our results achieve 3 orders of magnitude of improvement for $m_{\chi }$ larger than $80\mathrm{MeV}/{\mathrm{c}}^2$ compared to previous germanium-based $\chi \text{−}e$ results. We also present the most stringent $\chi \text{−}e$ cross-section limit to date among experiments using solid-state detectors for $m_{\chi }$ larger than $90\mathrm{MeV}/{\mathrm{c}}^2$ with heavy mediators and $m_{\chi }$ larger than $100\mathrm{MeV}/{\mathrm{c}}^2$ with electric dipole coupling. The result proves the feasibility and demonstrates the vast potential of a new $\chi \text{−}e$ detection method with high-purity germanium detectors in ultralow radioactive background.

• Received 10 June 2022
• Revised 25 August 2022
• Accepted 20 October 2022

DOI:https://doi.org/10.1103/PhysRevLett.129.221301

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Published by the American Physical Society