Pion-exchange contribution to the parity-violating asymmetry inp→pscattering

Charged pion exchange, resulting in an n${\Delta }^{++}$ state, contributes positively to the weak scattering asymmetry in longitudinally polarized p→p scattering at medium energy. This pion-exchange contribution combined with the traditional ρ and ω ‘‘elastic’’ contributions moves the total theoretical prediction into better agreement with the 800-MeV experimental data point. The pion-exchange contribution has both inelastic and elastic scattering components and is sizable even below the pion production threshold. Strong distortions enhance the magnitude of the effect.