CLOSE-COUPLING THEORY OF POSITRON HYDROGEN SCATTERING

The equations for positron-hydrogen scattering are written as a set of coupled momentum-space Lippmann-Schwinger equations. An explicit expr ession for the positronium formation matrix element that is suitable f or large-scale computation is derived. Elastic and positronium formati on cross sections are obtained in the coupled static model as a valida tion of the method. Calculations at energies below the hydrogen n = 2 threshold are used to study the convergence of observable quantities w ith increasing numbers of physical H and Ps states. At higher energies , a series of calculations including multiple hydrogen and positronium states are performed over the energy range from 1.0 to 4.0 Ryd. Cross sections for elastic scattering, excitation of the 2s and 2p hydrogen levels and positronium formation in the Is, 2s and 2p levels are repo rted.