An experimental and theoretical study of the momentum distribution of two photon annihilating positron–electron pairs in methane

The momentum distributions of annihilating positron–electron pairs have been measured in liquid and solid methane. Calculated momentum distributions generally assume that the positron wave function ψ+ = 1. This low-momentum, plane-wave representation of the positron is inadequate to describe the experimental distribution for high momenta. A ψ+ obtained by numerical integration of the ground-state radial Schrödinger equation is employed in the calculation and a good fit is observed with experiment for all momentum values.