Off-shell continuum distorted wave theory for positronium formation from noble gas atoms

The formation of ground-state positronium in collisions of positrons on noble gas atoms is considered. We report results obtained by means of the eikonal final state-continuum distorted wave (EFS-CDW) approximation for which off-shell distortion effects were taken into account. Comparison of the present theoretical total cross sections with experimental data reveals that distortion effects become important as the impact energy decreases.