Elastic D- and higher-partial-wave phase shifts in positron--hydrogen-atom collisions using Schwinger's principle

The Schwinger variational K matrix is used in the momentum space to calculate D- and higher-partial-wave phase shifts for the elastic scattering of positrons from atomic hydrogen below the pickup threshold in a discrete basis-set expansion, |un right-angle =|[1-exp(-pr1)](1+r1/2)exp(iki·r1)φi(r2) /(r12+a)n right-angle (n=1, . . .N). The values of the Schwinger D-wave phase shifts are found to be in close agreement with the Kohn variational results as for the S- and P-wave phase shifts. To the best of our knowledge, there are no other variational calculations for the higher-partial-wave phase shifts for l≥3. We have made use of these Schwinger variational phase shifts to compute accurate elastic differential and total cross sections at several positron energies. The differential cross section exhibits a sharp minimum at an intermediate scattering angle for incident momenta ki>0.3 a.u