Glauber Cross Sections for Excitation of the2 S1State of Helium by Electron and Positron Impact

Abstract

The recently proposed analytic methods, which reduce the Glauber amplitude for charged-particle—neutral-atom collisions to a one-dimensional integral representation involving modified Lommel functions, are used to evaluate the cross sections for the direct excitation of the $2 {}_{}{}^1{}_{}{}^{}S$ state of helium by electron and positron impact. Comparison is made with the Coulomb-projected Born approximation of Hidalgo and Geltman and the truncated eigenfunction-expansion method of Berrington, Bransden, and Coleman.