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 $\pi^- p \to X n \to e^+ e^- n$ 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 $^7{\rm Li}+p$ reaction. We also discuss a variety of other theoretically clean hadronic processes, such as $p+{\rm D(T)}$ fusion, as a promising source of $X$ particles.
Highlights
Extensions of the Standard Model (SM) by light and weakly coupled particles such as axions, axionlike particles, dark photons, etc., have been recognized as a generic possibility
The pion capture process π−p → Xn → eþe−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, axionlike particles, and other exotic states
Simple low-energy hadronic processes may provide an efficient way of probing light new physics
Summary
Extensions of the Standard Model (SM) by light and weakly coupled particles such as axions, axionlike particles, dark photons, etc., have been recognized as a generic possibility. In the SM, capture of a negatively charged pion on a proton leads to the production of a neutron which, to conserve momentum, recoils against a neutral boson with a mass less than about mπÆ 1⁄4 139.6 MeV, either a photon or π0. This should be contrasted with capture on nuclei. Weakly coupled bosons, X, with masses mX ≲ mπÆ can be produced in pion capture on a proton, π−p → Xn, if they couple to hadrons (or quarks) Production of these exotic bosons is relatively enhanced in π− capture on a proton as compared to nuclei for the same reason as π0 and γ production. V, and generalize our results to axionlike particles in the Appendix
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
