Search for dark matter decay of the free neutron from the UCNA experiment: N→χ+e+e-

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Abstract

It has been proposed recently that a previously unobserved neutron decay branch to a dark matter particle (χ) could account for the discrepancy in the neutron lifetime observed in experiments that use two different measurement techniques. 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. The summed kinetic energy (Ee+e-) from such events is used to set limits, as a function of the χ mass, on the branching fraction for this decay channel. For χ masses consistent with resolving the neutron lifetime discrepancy, we exclude this as the dominant dark matter decay channel at 5σ level for 100<Ee+e-<644keV. If the χ+e+e- final state is not the only one, we set limits on its branching fraction of <10-4 for the above Ee+e- range at >90% confidence level.

Original languageEnglish
Article number052501
JournalPhysical Review C
Volume97
Issue number5
DOIs
StatePublished - May 21 2018

Bibliographical note

Funding Information:
We are grateful for helpful discussions with B. Grinstein. This work is supported in part by the US Department of Energy, Office of Nuclear Physics (DE-FG02-08ER41557, DE-SC0014622, DE-FG02-97ER41042) and the National Science Foundation (NSF-1002814, NSF-1005233, NSF-1102511, NSF-1205977, NSF-1306997, NSF-1307426, NSF-1506459, and NSF-1615153). We gratefully acknowledge the support of the LDRD program (20110043DR) and the AOT division of the Los Alamos National Laboratory.

Publisher Copyright:
© 2018 American Physical Society.

ASJC Scopus subject areas

  • Nuclear and High Energy Physics

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