Many-body theory of positronium scattering and pickoff annihilation in noble-gas atoms

The many-body-theory approach to positronium (Ps) interactions with atoms developed by the authors [Phys. Rev. Lett. 120, 183402 (2018)] is applied to the noble-gas atoms He, Ne, Ar, Kr, and Xe. In this method, the Ps-atom interaction is described by the sum of the electron-atom and positron-atom correlation potentials (self-energies) and the screening of the electron-positron Coulomb interaction by the atomic electrons. Phase shifts and cross sections for elastic scattering are presented, along with values of the pickoff annihilation parameter ¹Z_eff, accounting for short-range electron-positron correlations via vertex enhancement factors. Comparisons are made with available experimental data for elastic and momentum-transfer cross sections and ¹Z_eff. Values of ¹Z_eff for He and Ne are found to be in near-perfect agreement with experiment; for Ar, Kr, and Xe, they are within 20% of measured values.