We report a search for light dark matter produced through the cascading decay of $\eta$ mesons, which are created as a result of inelastic collisions between cosmic rays and Earth’s atmosphere. We introduce a new and general framework, publicly accessible, designed to address boosted dark matter specifically, with which a full and dedicated simulation including both elastic and quasielastic processes of Earth attenuation effect on the dark matter particles arriving at the detector is performed. In the PandaX-4T commissioning data of $0.63\mathrm{tonne}·\mathrm{year}$ exposure, no significant excess over background is observed. The first constraints on the interaction between light dark matter generated in the atmosphere and nucleus through a light scalar mediator are obtained. The lowest excluded cross section is set at $5.9\times {10}^{-37}{\mathrm{cm}}^2$ for a dark matter mass of $0.1\mathrm{MeV}/c^2$ and mediator mass of $300\mathrm{MeV}/c^2$. The lowest upper limit of $\eta$ to the dark matter decay branching ratio is $1.6\times {10}^{-7}$.

• Received 11 January 2023
• Revised 26 April 2023
• Accepted 28 June 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.041001

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society