Correlation Effects in Differential Electron-Emission Spectra obtained from Double Ionization of He by Fast Au ⁵³⁺ Impact

We have measured and calculated doubly differential electron-emission cross sections (DDCS s) for well-defined degrees of target ionisation in 3.6 MeV/amu Au53þ þHe collisions. The calculations are based on the continuum distortedmwave with eikonal initial state approximation. We focus on DDCS s obtained in coincidence with double ionisation of the target, and investigate different models for the final two-electron continuum state. Whereas the results of an analysis within the independent particle model overestimate the experimental data badly, we find reduced DDCS s when electron correlation effects are included in a relatively simple fashion. The comparison between theoretical and experimental results indicates that the effective strength of the electron repulsion differs in close and distant collisions