Positronium formation in positron-helium collisions with a screened Coulomb interaction

A study is conducted on positronium (Ps) formation in positron-helium collisions under the effect of a Coulomb screening, e+ + He(1s2) → Ps(100) + He+(100), using the second-order distorted-wave approximation (DWA) and taking into consideration the screened dipole polarisation potential at low and intermediate incident positron energies in the range, 6-500 eV. The theoretical model for the scattering calculation is fairly accurate and predicts a number of interesting features in the total and differential cross sections for the screening parameter, μ = 0.0-0.4. The existence of resonances in the S-, P-, D- and F-partial waves has been reported in this work. Surface plots of the total and differential cross sections have also been presented to illustrate the interesting nature of the Ps formation in this scattering process. (authors)