Narrowing in on the Hadronic Weak Interaction: The Final Results of the NPDGamma Experiment

The weak interaction between nucleons has been of interest for nearly 50 years but is still not well described. The electroweak sector of the Standard Model describes the weak interaction of W and Z bosons with quarks and hadrons. This weak interaction causes small, but observable parity-violating signals in certain observables, such as spin-momentum correlations. But since the weak interaction between hadrons contains both the strong and weak interaction, the unsolved non-perturbative nature of QCD makes a direct calculation impossible. Instead, many theories have parametrized the Hadronic Weak Interaction (HWI) in terms of meson exchange degrees of freedom or S-P amplitudes as low energy constants. The theoretical difficulties have motivated few-body, low energy experiments, where there is little or no nuclear structure error. The NPDGamma experiment has completed one of these experiments and, for the first time, leads to a determination of one of the coupling constants as well as a constraint on others. The NPDGamma experiment and analysis will be discussed as well as the landscape and future of the HWI.