Parity violation in proton scattering: low energy region

Measurements of the parity-violating longitudinal analyzing power, Az, in the scattering of low-energy protons (Ep < 50 MeV) are reviewed. The experiments are based on the determination of the relative scattering cross sections σ+ and σ− for incident protons of positive and hegative helicity, respectively. The first results were reported from Los Alamos, where a significant analyzing power [Az = (−1.7 ± 0.8) × 10−7] was found for p–p scattering at 15 MeV. All other results are for a proton energy near 45 MeV, primarily by the group working at Schweizerisches Institut für Nuklearforschung, which recently reported a new, very accurate result for p–p scattering of Az = (−1.50 ± 0.22) × 10−7. A review is presented of the methods that have been developed by this group over the last 10 years to reduce systematic errors in the determination of Az to a few times 10−9.