Author:
Sun X.,Adamek E.,Allgeier B.,Blatnik M.,Bowles T.J.,Broussard L.J.,Brown M.A.-P.,Carr R.,Clayton S.,Cude-Woods C.,Currie S.,Dees E.B.,Ding X.,Filippone B.W.,García A.,Geltenbort P.,Hasan S.,Hickerson K.P.,Hoagland J.,Hong R.,Hogan G.E.,Holley A.T.,Ito T.M.,Kneckt A.,Liu C.-Y.,Liu J.,Makela M.,Mammei R.,Martin J.W.,Melconian D.,Mendenhall M.P.,Moore S.D.,Morris C.L.,Nepal S.,Nouri N.,Pattie R.W.,Galván A.P.,Phillips II D.G.,Picker R.,Pitt M.L.,Plaster B.,Ramsey J.C.,Rios R.,Salvat D.J.,Saunders A.,Sondheim W.,Sjue S.,Slutsky S.,Swank C.,Swift G.,Tatar E.,Vogelaar R.B.,VornDick B.,Wanchun W.,Wang Z.,Wexler J.,Womack T.,Wrede C.,Young A.R.,Zeck B.A.
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- + ν̅e decays. The summed kinetic energy (Ee+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.