Preliminary results on Fierz Interference from the most-recent UCNA data

The Fierz Interference term, $b$ in the Standard Model expression of the neutron beta decay rate, probes Beyond Standard Model physics by acting as a test of scalar and tensor couplings. It manifests, experimentally, in neutron decay by modifying the decay beta energy spectrum. In the past, the Ultracold Neutron Asymmetry experiment (UCNA) has reported on several measurements of the beta decay asymmetry, $A$, in the expression above. UCNA measures the neutron decay products of a trap filled with polarized ultracold neutrons whose decay products are directed, by a 1 T magnetic field, to detectors on either side of this trap. Due to the precise energy reconstruction needed for $A$, UCNA is able to provide a measurement of the beta decay energy spectrum and, hence, a measure of $b$ as well. The UCNA collaboration has previously set limits on $b$ using an older dataset. Here, we provide an overview of analysis focused on the most recent two-year span of data taken for UCNA. Furthermore, we present the results of implementing new calibration and analysis techniques, including using the energy dependence of $A$ to extract $b$.