Near-threshold positron-hydrogen ionization

Ionization of hydrogen by positron impact near the breakup threshold is considered. The two-centre convergent close-coupling method is used. We find that convergence in the cross section is only practically obtained if two near-complete expansions are used, one centred around H and the other around Ps. The contribution to the breakup cross section becomes the same for both centres as the threshold is approached. The calculations are found to be in good agreement with the threshold law predicted by Ihra et al.. Presented at the 20th Few-Body Conference, Pisa, Italy, 10-14 September 2007. (author)