Double ionization of helium by antiprotons

Abstract

We have developed a calculational scheme, the forced impulse method, for going beyond the independent particle model in ion-atom collisions. Our first application has been to the double ionization of helium; this requires construction of double ionization pseudostates. Initial calculations yielded good agreement with experimental results on the double ionization by protons, antiprotons, and alpha particles in the MeV/amu collision energy regime, and in particular reproduced the observed difference in double ionization by protons and antiprotons. We report here the results of expanding the angular momenta included in our single-particle basis, double ionization cross sections for other two-electron targets, and impact parameter dependences. Emphasis is on what we learn from our calculations about the mechanism for double ionization, and the physical reason for the observed difference in double ionization by protons and antiprotons.