Probing for an ultralight dark photon from inverse Compton-like scattering

Abstract

The dark photon not only provides a portal linking dark sector particles and ordinary matter but also is a well-motivated dark matter candidate. We propose to detect the dark photon dark matter through the inverse Compton-like scattering process $p+{\ensuremath{\gamma}}^{\ensuremath{'}}\ensuremath{\rightarrow}p+\ensuremath{\gamma}$. Thanks to the ultrahigh energy primary cosmic rays, we find that such a method is able to probe the dark photon mass from ${10}^{\ensuremath{-}2}\text{ }\text{ }\mathrm{eV}$ down to ${10}^{\ensuremath{-}19}\text{ }\text{ }\mathrm{eV}$ with the expected sensitivity of eROSITA $X$-ray telescope, which can extend the current lower limit of dark photon mass from Jupiter's magnetic fields experiment by about three orders of magnitude.