High energy photoionization beyond the independent particle approximation

Using a perturbative approach to the independent particle approximation (IPA) breaking effects we find analytical equations which enable us to obtain the high energy behaviour beyond IPA. The IPA breaking contributions to the cross sections are expressed as the IPA matrix elements of relatively simple operators. The equations for the cross section ratios are shown to be valid over a broad energy interval. We also obtain the quantitative criteria, which enable us to predict which of the couplings are significant for the fixed values of the photon energy. We compare our perturbative results to our numerical calculations. Accounting for IPA breaking effects is shown either to eliminate or to diminish strongly the discrepancy between the experimental data and the results of IPA calculations.