Positronium formation for positron scattering from metastable hydrogen

Positronium (Ps) formation for positron impact on metastable hydrogen in 2s state has been studied by using the two-channel, two-center eikonal final state-continuum initial distorted wave (EFS-CDW) method. The differential, integrated, and total cross sections for Ps formation in different states have been calculated from each channel opening thresholds to high energy region. The results are compared with other theoretical calculations available in the literature. For Ps formation in s-state at intermediate and high energies, our results are in good agreement with the prediction of distorted wave theory. Those formed in p-states and the total Ps formation cross sections are reported for the first time. It is shown that the total Ps formation cross sections for positron scattering from H(2s) state are significantly larger at relatively low energies, while smaller at high energies, compared with those obtained from hydrogen in ground state.