Rearrangement collisions with polarized positron beams and molecular oxygen targets

Angular-momentum coupling and density-matrix techniques are used to study the formation of para- and ortho-positronium in rearrangement collisions involving a slow polarized positron beam and a molecular oxygen target. Spin scattering matrices are obtained by ensuring spin conservation in the interaction region, and spin density matrices for the incoming positron-oxygen system are constructed to include an angular dependence between the spin-quantization axes of the two incoming beams. The ratios of para- to ortho-positronium formation are given for the scattering process O2 + e+ → O2+ + Ps for an unpolarized as well as a polarized oxygen target. The variation from the statistical value of View the MathML source is predicted in both cases. Experimental verification should be possible with modest upgrading of existing positron beam facilities.