Single ionization of helium by intermediate and high energy protons in the parabolic quasi-Sturmians approach

We are interested in investigating single ionization of helium by intermediate and high energy protons. The aim is to further understand this fundamental process by looking at fully differential cross sections (FDCS) for which measurements are available (on a relative scale [1] for 1 MeV protons, and on an absolute scale [2] for 75 keV protons).Recently, we have introduced a parabolic quasi-Sturmian approach [3] for calculating ion-atom ionizing collisions. Within the method, the ionization amplitude is represented as a sum of products of basis amplitudes associated with the asymptotic behavior of the continuum states of the two noninteracting hydrogenic subsystems (e-, He+) and (p+, He+). The proton-electron interaction is treated as a perturbation in the Lippmann-Schwinger type equation for the three-body system (e-, He+, p+). This equation is solved numerically using separable expansions for the proton-electron potential.

FDCSs are calculated and compared with experimental data and with the results obtained with other methods, including the WPCCC and the 3C model. While a globally satisfactory picture is obtained, theory-experiment discrepancies subsist in particular for large values of the transferred momentum for the 75 keV set of data.

[1] Gassert H et al, Phys. Rev. Lett. (2016) 116, 073201.

[2] Schulz M et al, Phys. Rev. A (2006) 73, 062704.

[3] Zaytsev A S et al, Phys. Rev. A (2022), 105, 062818.