Low-energy electron scattering from caesium atoms -comparison of a semirelativistic Breit-Pauli and a full relativistic Dirac treatment

The discrepancies between a previous Breit-Pauli R-matrix calculation and a recent calculation using the Dirac Hamiltonian are further analysed and partially resolved. When comparable methods are applied to obtain the best possible target description in both approaches, a reduced Breit-Pauli formulation, with only the one-body spin-orbit operator included to account for relativistic effects explicitly, seems sufficient for an accurate description of most of the low-energy collision processes in this system. There remain, however, some interesting differences between the Breit-Pauli and the Dirac results for spin polarization and asymmetry functions, as well as for very sensitive resonance parameters. (author)