Search for anomalous decay of the free neutron using the UCNA experiment: n -> $\chi + e^+ + e^-$

The neutron lifetime is currently measured by two different types of experiments: 'beam' and 'bottle', which have a 4$\sigma$ discrepancy in measured lifetime. In January 2018, Fornal and Grinstein proposed to resolve this issue by introducing a dark sector particle, $\chi$, that could offer an alternative decay channel for the neutron. The proposed theory allows for a $e^+ e^-$ pair produced in addition to the hypothesized $\chi$. The UCNA (Ultra Cold Neutron Asymmetry) experiment is particularly sensitive to this decay signature. 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. 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, as a function of the mass of the $\chi$. In this talk, we present the analysis and set limits on this neutron dark matter decay channel.