Parity Violation in Hadronic Systems

Our present understanding of the AS=O hadronic weak interaction is based on a collection of high precision experiments in the two-nucleon system and light nuclei, which isolate the weak interaction via its parity-violating signature. The weak nucleon-nucleon interaction at low and intermediate energies is described in terms of a meson exchange model involving n, p and W mesons, with one strong and one weak vertex. Experiments have yielded significant but incomplete information on weak meson-nucleon couplings, which are in qualitative agreement with predictions based on the standard model, although the pion coupling is much weaker than expected. Studies of the p+p system have provided the most significant constraints on weak meson-nucleon couplings to date, through measurements of the helicity dependence of elastic scattering (A,); new results at low energy, plus the outcome of an intermediate energy experiment in progress at TRIUMF, will have significant impact on our knowledge of the weak nucleon-nucleon interaction. The present status of theory and experiment will be reviewed, with emphasis on experimental techniques and interpretation in the context of the standard model.