DIFFERENTIAL CROSS-SECTIONS FOR TARGET EXCITATION AND POSITRONIUM FORMATION IN POSITRON-HELIUM SCATTERING

Positronium formation and target excitation in positron-helium scatter ing have been investigated using the close-coupling approximation with realistic wave functions for the positronium and helium atoms. The fo llowing eight states have been used in the close-coupling scheme: He(1 s1s), He(1s2(1)s), He(1s2(1)p), He(1s3(1)s), He(1s3(1)p), Ps(1s), Ps(2 s), and Ps(2p), where Ps stands for the positronium atom. Calculations are reported of differential cross sections for elastic scatering,, i nelastic target excitation to He(1s2(1)s) and He(1s2(1)p) slates, and rearrangement transition to Ps(1s), Ps(2s), and Ps(2p) states for inci dent positron energies between 40 and 200 eV. The coincidence paramete rs for the transition to the He(1s2(1)p) state of helium are also repo rted and briefly discussed. [S1050-2947(98)05101-4].