Correlation effects in differential electron-emission spectra obtained from double ionisation of He by fast Au53+ 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 Au53+ + He collisions. The calculations are based on the continuum distorted wave 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