May 29, 2018 to June 3, 2018
Hyatt Regency Indian Wells Conference Center
US/Pacific timezone

Search for Anomalous Decay of the Free Neutron Using the UCNA Experiment: $n \to \chi + e^+ + e^-$

Jun 1, 2018, 6:30 PM
East Foyer (Hyatt Regency Indian Wells Conference Center)

East Foyer

Hyatt Regency Indian Wells Conference Center

44600 Indian Wells Lane, Indian Wells, CA 92210, USA
Board: 6
Poster TSEI Poster Session


Mr Xuan Sun (California Institute of Technology)


The neutron lifetime is currently measured by two different types of experiments: 'beam' and 'bottle'. These two measurement techniques have a $4\sigma$ discrepancy in measured lifetime. A recent paper proposes to resolve this issue by introducing a dark sector particle, $\chi$, that could offer an alternative decay channel for the neutron. This decay channel could resolve the discrepancy since beam experiments measure final decay products and bottle experiments measure remaining neutron population. The proposed theory allows for an $e^+ e^-$ pair produced in addition to a hypothesized $\chi$. The UCNA (Ultra Cold Neutron Asymmetry) experiment has sensitivity to this particular decay signature, since it would appear as a mono-energetic peak over a standard $\beta$ decay spectrum. In this experiment, polarized neutrons decay in a trap and their charged products are guided by a 1 T magnetic field to detectors on either side, thus effectively giving $4\pi$ detection coverage. Timing information and energy reconstruction is done on each $\beta$ decay. We use results from the UCNA experiment's 2012–2013 dataset to set limits on the branching fraction of this decay channel. In the case of a candidate $e^+ e^-$ pair, the summed reconstructed energy from both sides is used to set limits on the branching ratio of this decay channel, as a function of the mass of the hypothesized $\chi$. We present an overview of the calibration process and the limits on a neutron dark decay channel set by the UCNA experiment.
E-mail [email protected]
Collaboration name UCNA Collaboration
Funding source 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 (1002814, 1005233, 1205977, 1306997 1307426, 1506459, and 1615153).

Primary author

Mr Xuan Sun (California Institute of Technology)

Presentation materials