Fragmentation of positronium in collision with He atoms: A classical theoretical approach

The classical trajectory Monte Carlo method was applied to the description of the fragmentation of the positronium (Ps) in collision with He atoms. The collision system was simplified to a three-body system consisting of the electron and the positron of the Ps, as well as the He atom that was considered as a structureless particle. The interaction of the e- and e+ with the He was approximated by a static, fully screened Coulomb potential. The calculations were carried out for collision energies 13, 18, 25, and 33 eV. The obtained total break-up cross sections and the longitudinal energy distributions of the emitted positrons were compared with the recent experimental results of Armitage et al. [Phys. Rev. Lett. 89, 173402 (2002)]. The present theory overestimates the measured cross sections by a factor of 1.6-2.5, but it correctly reproduces the peak found by Armitage et al. in the positron spectra at about half of the residual Ps energy