Discrepancy between theory and experiment in double ionization of helium by fast electrons

We compute fully differential cross sections for double ionization of helium by electrons, within the high-impact- energy and low-momentum transfer regimes, using the generalized Sturmian functions approach. Our results are converged relative to the total angular momentum and variable domain size. The method shows very good agreement with convergent close coupling calculations performed by Kheifets et al. [J. Phys. B 32, 5047 (1999)] for all ejection angles for the two electron emission energies considered in the experiments reported in that contribution. Both theoretical methods provide fully differential cross sections that require the same upscaling factors to compare with experimental data and are based on a first-order Born model for the projectile-target interaction. Since that reference was published, there were several theoretical efforts to account for the absolute scale of the experimental results, but agreement in the cross-section magnitude was not achieved even between theories. With the present contribution we conclude that the first-order Born model is now adequately solved, shifting the magnitude controversy towards either the experimental data and/or the addition of higher degrees of projectile-target interaction to the calculation.