A PARTIAL-WAVE ANALYSIS OF POSITRONIUM FORMATION IN POSITRON-HELIUM SCATTERING

Calculations are made of the s-, p- and d-wave contributions to the po sitronium formation cross section for positron-helium scattering in th e Ore gap. The Kohn variational method is used with very flexible tria l functions, and the results obtained are believed to have converged t o within 20% of their exact values. In contrast to the findings of a r ecent analysis of the experimental results for positronium formation, that the p-wave contribution is dominant, the present results show tha t the d-wave contribution is the largest throughout most of the Ore ga p. Nevertheless, the total positronium formation cross sections, calcu lated from the sum of the variational s-, p- and d-wave contributions and the results of the Born approximation for all higher partial waves , display a very similar energy dependence to that of the experimental results, but are approximately 30% smaller.