Partial-wave analysis of particular peaks in total scattering cross sections caused by a single partial wave

Abstract

Certain broad low-energy peaks in the total cross sections relevant for electron-atom scattering are studied and found to be caused by a single partial wave. Such peaks are associated here with complex orbital angular momentum (Regge) pole trajectories. At the peak energies these S-matrix poles are in some neighborhood of an integer value and at the same time near its maximum real part value as a function of energy. Such peaks are found to have no time delays. Results are presented for the Dirac equation using three rational function Thomas-Fermi potential models, all with the same behavior at large and small radial distances.