Low-energy S- and P-wave Positronium-Hydrogen Collisions*

Positronium-atom scattering is of experimental interest. We have investigated low-energy positronium-hydrogen scattering, a fundamental four-body Coulomb process. We computed the S- and P-wave phase shifts using a number of variants of the Kohn variational method. For the S-wave, we implemented various techniques to overcome linear dependence problems. Our results compare favorably with earlier Kohn variational calculations [1]. We determined the S-wave scattering length and effective range using a quantum defect theory for the van der Waals interaction [2]. \\[4pt] [1] P. Van Reeth and J. W. Humberston, J. Phys. B {\bf 36}, 1923 (2003), Nucl. Intrum. and Methods Phys. Res. B {\bf 221}, 140 (2004).\\[0pt] [2] Bo Gao, Phys. Rev. A {\bf 58}, 4222 (1998).