New physics via pion capture and simple nuclear reactions

Abstract

Light, beyond-the-standard-model particles $X$ in the 1-100 MeV mass range can be produced in nuclear and hadronic reactions but would have to decay electromagnetically. We show that simple and well-understood low-energy hadronic processes can be used as a tool to study $X$ production and decay. In particular, the pion capture process ${\pi }^{-}p\to Xn\to e^{+}{e}^{-}n$ can be used in a new experimental setup to search for anomalies in the angular distribution of the electron-positron pair, which could signal the appearance of dark photons, axion-like particles and other exotic states. This process can be used to decisively test the hypothesis of a new particle produced in the ${}^7\mathrm{Li}+p$ reaction. We also discuss a variety of other theoretically clean hadronic processes, such as $p+\mathrm{D}(\mathrm{T})$ fusion, as a promising source of $X$ particles.

Comments: 9 pages, 5 figures, typo in acknowledgments corrected