Parity violation in the compound nucleus

Parity Violation in the compound nucleus is reviewed as an example of a wid er class of phenomena: The breaking of st discrete symmetry by a weak inter action in a stochastic or chaotic quantum system. Generically, enhancement factors amplify the signal for symmetry breaking, and the stochastic proper ties anew the strength of the symmetry-breaking interaction to be inferred from that signal without the need to know the wave functions of individual states. We describe recent experiments on parity violation that have been u ndertaken in this spirit. The scattering of spin-polarized neutrons by medi um-weight and heavy nuclei provides signals for parity violation at the per cent level. The statistical analysis of the data yields values for the spre ading width around 10(-6) eV, in keeping with theoretical expectations. We discuss open problems and possible future directions. [S0034-6861(99)00201- 9].