ElasticD- 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〉 ={}[1-exp(-pr₁)](1+r₁/2)exp(ikᵢ{·}r₁)φᵢ(r₂) /(r₁₂+a)ⁿ〉 (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.