Orthopositronium-sodium scattering using the close-coupling approximation in the integral representation

Abstract

We investigate the scattering of orthopositronium by atomic sodium target at low and medium energies (up to 50 eV) using target-elastic and projectile-elastic close-coupling approximations (CCA) having different basis sets together with the static-exchange model. The low-energy elastic-scattering parameters are found to be consistent and the estimated binding energy for NaPs (in spin-singlet scattering) runs from 0.0042--0.0052 a.u. compared to value 0.005 892 a.u. obtained by using stochastic variational method [G. Ryzhikh and J. Mitroy, J. Phys. B 31, L401 (1998)]. The elastic cross sections as obtained by different CCA models, except the static-exchange one, differ very marginally among themselves in the energy range 0.017--25 eV and 15 eV, onwards all the partial cross sections are very close to the corresponding exchange plane-wave estimates. At higher energies (above 15 eV), it is found that the major contribution to the total cross section comes from the positronium inelastic channels.