Electron exchange model potential: Application to positronium-helium scattering

The neutral Ps beam provides a great deal of advantage over charged projectiles as a probe to study the structure of atoms, molecules and surface. Recently, there have been a great deal of interest in positronium(Ps-) atom scattering due to the improvement of Ps sources and Ps beams. Total scattering cross section of ortho Ps, which has a larger lifetime than para Ps, have been measured for various targets [1,2] with an objective of understanding the Ps-interaction dynamics with matter. Among all Ps-atom systems, the positronium-hydrogen (Ps-H) system is the simplest and is of special theoretical interest [3]. However, due to experimental difficulties in obtaining nascenthydrogen atomic target there has been no experimental study of Ps-H scattering. The next most complicated Ps-atom system is the positronium-helium (Ps-He) system in which there are good experiments on total cross section [1,2]. However, there are no theoretical studies [4–7] which can account for the measured total cross sections of ortho Ps-He scattering . We address the present study towards an understanding of the measured total cross sections of Ps-He scattering at low and medium energies using a suitably developed model exchange potential. The interaction of neutral Ps atom with neutral atom or molecule is very much different from that of charged