Theoretical analysis on fully differential cross sections for C⁶⁺ impact ionization of helium

Fully differential cross sections (FDCS) are calculated within a four-body model for single ionization of helium by C⁶⁺ impact at the incident energy of 100 MeV/a.u. (atomic unit). The results are compared with experimental data and other theoretical predictions. It is shown that our results are in very good agreement with experiment for three small momentum transfers in the scattering plane; however, some significant discrepancies are still present at the largest momentum transfer in both the scattering plane and the perpendicular plane. In actuality, the problem has not been explained by the theory during the last decade. Accordingly, the contributions of different scattering amplitudes to FDCS are analyzed. It is found that for the largest momentum transfer the cross section arising from a destructive interference of the three amplitudes is much smaller than the experimental data. However, the cross section due to the constructive interference of two scattering amplitudes between projectile—ionized electron interaction and projectile—passive electron interaction almost approaches the experimental data.