ELASTIC D-PARTIAL-WAVE AND HIGHER-PARTIAL-WAVE PHASE-SHIFTS IN POSITRON-HYDROGEN-ATOM COLLISIONS USING SCHWINGERS PRINCIPLE

The Schwinger variational K matrix is used in the momentum space to ca lculate D- and higher-partial-wave phase shifts for the elastic scatte ring of positrons from atomic hydrogen below the pickup threshold in a discrete basis-set expansion, \u(n) > xp(-pr1)](1+r1/2)exp(ik(i).r1)p hi(i)(r2)/(r12+a)n] > (n = 1,... N). The values of the Schwinger D-wav e phase shifts are found to be in close agreement with the Kohn variat ional results as for the S- and P-wave phase shifts. To the best of ou r knowledge, there are no other variational calculations for the highe r-partial-wave phase shifts for l greater-than-or-equal-to 3. We have made use of these Schwinger variational phase shifts to compute accura te elastic differential and total cross sections at several positron e nergies. The differential cross section exhibits a sharp minimum at an intermediate scattering angle for incident momenta k(i) > 0. 3 a.u.