Double ionization of helium by slow antiprotons

Coupled-states calculations with large target-centred basis sets have been used to compute ionization probabilities and cross sections for at collision energies down to 10 keV. The results are in good agreement with recent theoretical calculations based on numerical solution of the time-dependent Schrödinger equation but there are no experimental data. Both an independent particle model and an independent event model were used to carry out calculations for . These results are in good agreement with experiment at 40 keV and above but differ at lower energies. The impact-parameter-dependent probabilities for these collisions were used in the independent event model to calculate helium double-ionization cross sections and excellent agreement was found with experimental measurements between 13 and 200 keV, but this simple way of treating correlation fails at higher collision energies.