Parity nonconservation has been studied in elastic $p\alpha$ scattering at 46 MeV with longitudinally polarized protons. The longitudinal analyzing power averaged over the range of laboratory scattering angles of roughly 30° to 60° is found to be $A_z=(-3.3\mathrm{}\pm 0.9)\times {10}^{-7\mathrm{}}$. This result and measurements in other light nuclear systems are used to determine weak meson-nucleon coupling constants.

• Received 9 October 1984

DOI:https://doi.org/10.1103/PhysRevLett.54.170