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Four-body charge transfer processes in proton–helium collisions

Recent advancements in experimental techniques now allow for the study of fully differential cross sections (FDCS) for four-body collisions. The simplest four-body problem is a charged particle collision with a helium atom, in which both atomic electrons change state. This type of collision can result in many different outcomes, such as double excitation, excitation ionization, double ionization, transfer excitation, transfer ionization and double charge transfer. In this paper, we compare absolute experimental proton–helium FDCS for transfer excitation with the fully quantum mechanical 4BTTE (four-body transfer with target excitation) model. This model was previously used to study TTE for proton energies between 25 and 75 keV and reasonable agreement was found with the experimental data for large scattering angles, but not small angles. Since this is a first-order model, which contains contributions from all higher order terms, one would expect improved agreement with increasing energy and the purpose of this work was to look at higher energies. We found that the agreement with the magnitude of the experimental data became worse with increasing energy while the agreement with the shape of the data was reasonably good. Consequently, we conclude that the model contains the physical effects that determine the shape but not the magnitude of the cross section.