Constraints on Solar Reflected Dark Matter from XENON1T and XENONnT Data

We report on a search for sub-GeV dark matter upscattered via the solar reflection mechanism in the heavy mediator scenario. Under the standard halo model, keV–MeV dark matter produces nuclear recoils with energies below the detection threshold of liquid xenon time projection chambers. We enhance sensitivity to low-mass dark matter (DM) by considering dark matter–electron scattering, employing dedicated event selections to reduce the detection threshold and exploiting the additional kinetic energy imparted to the dark matter particle by solar upscattering. Using XENON1T ionization-only and XENONnT low-energy electronic recoil datasets, we exclude previously unconstrained DM-electron scattering cross section for masses between 4.6 and 20  keV/⁢𝑐$^2$ and between 0.2 and 2  MeV/𝑐$^2$, reaching a minimum of 3.41×10$^{−39}$  cm$^2$ for a mass of 0.3  MeV/𝑐$^2$ at 90% confidence level.