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Published December 13, 2019 | Published
Journal Article Open

Search for neutron dark decay: n → χ + e⁺e⁻

Abstract

In January, 2018, Fornal and Grinstein proposed that a previously unobserved neutron decay branch to a dark matter particle (χ) could account for the discrepancy in the neutron lifetime observed in two different types of experiments. One of the possible final states discussed includes a single χ along with an e⁺e⁻ pair. We use data from the UCNA (Ultracold Neutron Asymmetry) experiment to set limits on this decay channel. Coincident electron-like events are detected with ∼ 4π acceptance using a pair of detectors that observe a volume of stored Ultracold Neutrons (UCNs). We use the timing information of coincidence events to select candidate dark sector particle decays by applying a timing calibration and selecting events within a physically-forbidden timing region for conventional n → p + e⁻ + ν̅_e decays. The summed kinetic energy (E_(e⁺e⁻)) from such events is reconstructed and used to set limits, as a function of the χ mass, on the branching fraction for this decay channel.

Additional Information

© 2020 The Authors, published by EDP Sciences. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). Published online 13 December 2019. his work is supported in part by the US Department of Energy, Office of Nuclear Physics (DE-FG02-08ER41557, DESC0014622, DE-FG02-97ER41042) and the National Science Foundation (1002814, 1005233, 1205977, 1306997, 1307426, 1506459, and 1615153). We gratefully acknowledge the support of the LDRD program (20110043DR), the AOT division of the Los Alamos National Laboratory, and helpful discussions with B. Grinstein.

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