The positron-hydrogen system at low energies

Abstract

Calculations of low-energy positron-hydrogen and positronium-proton scattering using the close coupling method are reported at energies below the ionization threshold. The channel space included six hydrogen (1s, 2s, 2p, 3s, 3p and 3d) and six positronium (1s, 2s, 2p, 3s, 4s and 3p) states. Comparisons with more accurate calculations demonstrate that this model should give integrated cross sections accurate to 10%. Cross sections are computed with a fine energy mesh and a total of 11 resonances associated with the H(n=2) and Ps(n=2) thresholds have been identified and the resonance positions and widths determined. Calculations of the total cross section and the positronium formation cross section for positron-hydrogen scattering are consistent with the available experimental data. Cross sections for elastic scattering in the Ps(1s)-p entrance channel are dominated by a strong polarization potential and vary from 1000 pi a02 at threshold to 15 pi a02 at 1.0 Ryd. Cross sections for the Ps(1s)+p to e++H(nl) rearrangement collision are also reported since these provide baseline data relevant to experiments aimed at making antihydrogen atoms. Differential cross sections for elastic Ps(1s)-p and e+-H(1s) scattering and for electron transfer to the hydrogen atom ground state are also reported at selected energies.