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

The Neutron OPtics Time Reversal EXperiment (NOPTREX) Collaboration seeks to investigate potential time-reversal (T) symmetry violations in neutron-nucleon forward scattering within parity (P) violating nuclear resonances. Given that the theoretically proposed T-violating cross-section is directly related to a P-violating cross-section, precise spectroscopy of these resonances is crucial. The 0.734 eV p-wave resonance in 139La, known for its significant 10% P-violation effect, is a prime candidate for the NOPTREX experiment. Our objective is to measure this effect in 139La with 1% precision, surpassing previous room temperature measurements by utilizing cryogenic targets at 15K to minimize Doppler broadening and extending the measurement period to reduce statistical uncertainty. This experiment was carried out at Los Alamos National Laboratory between 2017 and 2019. This presentation will outline the experimental setup, efforts to limit systematic uncertainties, data analysis procedures, and the results obtained.