Detecting Dark Photon with Reactor Neutrino Experiments

We propose to search for light $U(1)$ dark photons, $A'$, produced via kinetically mixing with ordinary photons via the Compton-like process, $\gamma e^- \rightarrow A' e^-$, in a nuclear reactor and detected by their interactions with the material in the active volumes of reactor neutrino experiments. We derive 95\% confidence-level upper limits on $\epsilon$, the $A'$-$\gamma$ mixing parameter, $\epsilon$, for dark-photon masses below 1$\sim$MeV of $\epsilon~< ~1.3\times 10^{-5}$ and $\epsilon~<~2.1\times 10^{-5}$, from NEOS and TEXONO experimental data, respectively. This study demonstrates the applicability of nuclear reactors as potential sources of intense fluxes of low-mass dark photons.