Proton angular distributions and highly differential cross sections for ionization of helium by proton impact

The eikonal distorted-wave method is applied to single ionization in proton-helium collisions at laboratory energies of 300 keV, 500 keV, 1 MeV, and 3 MeV. The angular distributions of scattered protons agree well with recent experimental results, showing substantial improvement over the plane-wave Born approximation especially at large scattering angles {Θ}. The momentum distributions of the ejected electrons at fixed values of {Θ} are calculated. In particular, those of the electrons ejected mainly in binary proton-electron collisions are studied in detail. The momentum distributions of the recoil He⁺ ions at fixed values of {Θ} are also discussed by comparing with the results of recent coincidence measurements. At such small {Θ} at which the plane-wave Born and the eikonal distorted-wave approximations give nearly the same cross sections and are expected to be accurate, these approximations lead to average momenta of recoil ions significantly lower than the measured values.