Low energy o-Ps-o-Ps elastic scattering using a simple model

A simple model is employed to investigate o-Ps-o-Ps (positronium-positronium) scattering at low energies. This model contains the effect of exchange explicitly and a model long range potential in the framework of static-exchange model. These two physical features are of key importance in Ps-Ps (atom-atom) scattering system. S-wave triplet-triplet and singlet-singlet scattering lengths and corresponding phase shifts up to the incident momentum k = 0.5 a.u. are in excellent agreement with those yielded by most elaborate and theoretically sound predictions. (authors)