Positronium scattering from Kr and Xe at low energies

The scattering of orthopositronium from Kr and Xe is investigated with the fixed core stochastic variational method. The scattering lengths for Ps-Kr and Ps-Xe scattering in the fixed core approximation are 3.18a₀ and 3.82a₀, respectively. Inclusion of core-polarization potentials leads to a significant reduction in the scattering lengths. The Ps-Kr and Ps-Xe scattering lengths were 1.98a₀ and 2.29a₀ for polarization potentials that were tuned to an average of the model electron-atom and positron-atom scattering lengths for the respective atoms. Other choices of the polarization potential resulted in scattering lengths that could be larger by 0.3a₀ or smaller by 0.8a₀. The pick-off annihilation parameter ₁Z_eff has also been computed as part of the analysis. The present values of ₁Z_eff are about 3 to 10 times smaller than the accepted experimental values since short-range electron-positron correlations were ignored when the annihilation matrix element was evaluated.