A Precision Measurement of the Parity Violation Present in the 0.734 eV p-wave Resonance in $^{139}$La Using the 'Double Lanthanum' Technique: Preliminary Results and Analysis

The Neutron OPtics Time Reversal EXperiment (NOPTREX) Collaboration aims to measure potential time-reversal (T) violating processes in neutron-nucleon forward scattering interactions in parity (P) violating nuclear resonances. Because the proposed theoretical T-violating cross-section is directly proportional to a P-violating cross-section, precision spectroscopy of these resonances is of critical importance. In particular, the 0.734 eV p-wave resonance in $^{139}$La exhibits a well known ~10\% P-violation effect, making it an outstanding candidate for the NOPTREX experiment. We aim to measure this effect in $^{139}$La to 1\% precision, improving upon previous (room temperature) measurements by using cryogenic targets (15K) to reduce Doppler broadening effects as well as running for a longer period of time to reduce statistical uncertainty. This experiment was conducted at Los Alamos National Laboratory in 2017-2019. This talk will briefly cover the experimental setup, the efforts to constrain systematic uncertainties, the data analysis process, and preliminary results.