Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved dark matter decay mode, nX+γ. We perform a search for this decay mode over the allowed range of energies of the monoenergetic γ ray for X to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify γ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Monte Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting γ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97% confidence.

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Published in Physical Review Letters, v. 121, issue 2, 022505, p. 1-5.

© 2018 American Physical Society

The copyright holder has granted the permission for posting the article here.

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This work was supported by the Los Alamos Laboratory Directed Research and Development (LDRD) office (Grant No. 20140568DR), the LDRD Program of Oak Ridge National Laboratory, managed by UT-Battelle, Limited Liability Corporation (LLC) (Grant No. 8215), the National Science Foundation (Grants No. 130692,No. 1307426, No. 161454, No. 1506459, and No. 1553861), the Indiana University (IU) Center for Space Time Symmetries (IUCSS), and United States Department of Energy (U.S. DOE) Low Energy Nuclear Physics (Grants No. DE-FG02-97ER41042, No. DE-SC0014622, and No. DE-AC05-00OR22725).

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