Evolution of e--He (e, 2e) differential cross sections at 64.4 eV with different geometries

The distorted wave Born approximation is used to calculate the He (1s(2)) (e,2e) triple differential cross section at 64.6 eV in the different kinematical geometries, namely: (i) non-coplanar symmetric scattering angles with symmetric as well as asymmetric energy sharing; (ii) coplanar asymmetric with one scattering angle fixed and the other one variable; (iii) coplanar asymmetric with angular separation between the two outgoing electrons constant. The spin average static exchange (with the exchange part taken in equivalent local approximation) interaction potential is used. Two important characteristic features of the observed differential cross sections in non-coplanar geometry, namely: (i) a common point in the cross section curve for the two outgoing electrons at 90 degrees with the incident direction projected on the detection plane for all the energy sharing states and (ii) a deep minimum for the angular separation of 67.5 degrees between the detection plane and the electron beam have been fully supported. In coplanar asymmetric geometry, results are in agreement with the scaled up (by a constant factor of 1.8) convergent close-coupling cross sections.