Nucleon-nucleon parity violation experiments

Measurements of parity-violating longitudinal analyzing powers A(z) (normalized asymmetries) in polarized proton-proton scattering and in polarized neutron capture on the proton (n - p --> d - gamma) provide a unique window on the interplay between the weak and strong interactions between and within hadrons. Several new proton-proton parity violation experiments are presently either being performed or are being prepared for execution in the near future: at TRIUMF at 221 MeV and 450 MeV and at COSY (Forschungszentrum Julich) in the multi-GeV range. A. new measurement of the parity-violating gamma ray asymmetry with a ten-fold improvement in the accuracy over previous measurements is being developed at LANSCE. These experiments are intended to provide stringent constraints on the set of six effective weak meson-nucleon coupling constants, which characterize the weak interaction between hadrons in the energy domain where meson exchange models provide an appropriate description. The 221 MeV p-p experiment is unique in that it selects a single transition amplitude ((3)P(2) - (1)D(2)) and consequently constrains the weak meson-nucleon coupling constant h(rho)(pp). The n - p --> d - gamma experiment is mainly sensitive to the weak pion-nucleon coupling constant f(pi). Together with the existing p - p parity violation experimental results one may be able to delineate the various weak meson-nucleon coupling constants. The TRIUMF 221 MeV p - p, parity violation experiment will be described in some detail. Other parity violation nucleon-nucleon and nucleon-very-light-nucleus experiments are commented on. The anomalous result obtained at 6 GeV/c on a water target requires that a new multi-GeV p - p parity violation experiment be performed.