Spin exchange in scattering with polarized orthopositronium beams

Abstract

We study electron and positron exchange without a spin flip in a single collision between two polarized orthopositronium beams. We use angular-momentum coupling and density-matrix techniques to calculate the probabilities of obtaining only parapositronium, both para- and orthopositronium or only orthopositronium, after the collision. The probabilities are functions of the angle between the polarization vectors of the beams and scattering amplitudes labeled with total electron spin and total positron spin. The real parts of the scattering amplitudes and products of the polarization tensors for the beams are given in terms of the probabilities for certain angles and initial spin orientations. We show that quenching probabilities for different transitions and the spin-exchange quenching cross section depend on the angle, but the ratio of the total quenching probability to the total probability for positronium scattering does not.