Coupling between positron-atom scattering channels above the first inelastic threshold

Experimentally determined cross sections for the elastic scattering of positrons by argon and xenon atoms have been found to exhibit a steplike increase at the first inelastic threshold energy-i.e., that for positronium formation. Rather than supporting the existence of a cusplike behavior predicted theoretically, this feature, which is more pronounced for xenon, suggests the existence of an intermediate virtual positronium state which enhances the elastic interaction probability.