Zero-crossing angle in the np analyzing power at medium energies and its relation to charge symmetry

The angle at which the analyzing power for free np scattering becomes zero, the zero-crossing angle θ₀, has been measured simultaneously for the →np and n→p scattering processes at 425, 565, and 665 MeV incident neutron energies. A rather strong energy dependence of the zerocrossing angle is found. Knowledge of this energy dependence is important in designing an experiment which tests for charge symmetry breaking forces by comparing high precision measurements of θ₀(→np) and θ₀(n→p).[NUCLEAR REACTIONS $p(n,p)n$, E=425,565, and 665 MeV; polarized neutron beam, polarized proton target; measured analyzing powers A(E,θ); deduced zero-crossing angles; charge symmetry.]