Elastic differential cross section and critical point for positron-hydrogen collisions

A detailed study is made of the elastic differential cross section in positron-hydrogen collisions using the accurate Schwinger variational results for partial waves up to l=19 of the preceding paper [Ghoshal and Mandal, Phys. Rev. A, 72, 042709 (2005)]. Dramatic behavior of the differential cross section is evident in the surface plots, suggesting interference of partial-wave contributions at small and large scattering angles for the appearance of rich structure. It is found that the behavior of the critical point basically characterizes the nature of the differential cross section. Further interferences of the scattered waves for different angular momentum states produced by the interaction between the incoming positron and the target hydrogen atom determine such behavior and consequently build up the nature of the differential cross section. These findings reveal the remarkable fact that positron-hydrogen scattering almost does not occur in the direction around 87.3 degrees at an incident energy of about 3.4 eV, corresponding to incident positron momentum of 0.5 atomic units.