Constraints on millicharged particles from nuclear gamma-decays

Abstract

We consider nuclear gamma decays and ${\hat{I}}^3$-emitting reactions that can be an efficient source of hypothetical millicharged particles ($\ddot{I}‡$). In particular, we revisit the production of millicharged particles in nuclear reactor environment, pointing out that ${\hat{I}}^3$ cascades from ${}^{239}$U is an overlooked yet a powerful source of $\ddot{I}‡\bar{\ddot{I}}‡$ pairs. This leads to an increased flux compared to previous studies. We then apply new estimates of the flux to derive novel limits on the value of millicharge, $\epsilon =Q_{\ddot{I}}‡/e$, from the electron recoil searched for in a variety of experiments placed in proximity to the reactor cores. The derived limits on $\epsilon$ are the strongest in the interval of masses $\sim 0.7-2$ MeV. We also derive the MCP flux from the Sun and point out potential sensitivity of the low-threshold dark matter search experiments.

19 pages, published version