Second-order Born cross sections for positronium formation in positron-hydrogen collisions.

Abstract

The second-order Born cross sections of positronium formation are calculated for positron-hydrogen collisions in the energy region below 100 eV and compared with the recent measurement of Sperber et al. [Phys. Rev. Lett. 68, 3690 (1992)]. Better agreement is achieved above 25 eV than other existing theoretical values including elaborate close-coupling calculations. This result implies that continuum states that are not taken into account fully in other theoretical calculations are contributing significantly to positronium formation through a second-order process.