Fierz Interference results and analysis from most-recent UCNA data

The Fierz Interference term, $b$ in the Standard Model expression of the neutron beta decay rate, acts as a probe of beyond Standard Model physics due to its sensitivity to scalar and tensor couplings. Experimentally, $b$ manifests as an energy distortion in the neutron beta decay energy spectrum. Furthermore, in the beta decay asymmetry parameter, the presence of a non-zero $b$ introduces an energy-dependent distortion in $A_0$, yielding $A_{0,b} (E)$. Using the most recent $A_0$ data from the Ultracold Neutron Asymmetry experiment (UCNA), located at Los Alamos National Laboratory (LANL), we extend the previous results on direct $b$ extraction via the energy dependence of $A_{0,b} (E)$. Furthermore, we present a supplementary analysis of the direct spectral measurements of the neutron beta decay and extract a $b$ value from that as well. Finally, we compare and contrast the advantages and limitations of these two methods of $b$ extraction.