The production of positronium and its resonant scattering

The total cross section of positronium scattering from a variety of atoms and molecules has been found to be unexpectedly close to that of a bare electron moving at the same velocity, despite Ps being neutral and having twice the mass [Science 330, 789 (2010)]. This behaviour appears to extend to velocities where effects such as the Ramsauer-Townsend minima and shape resonances occur for electrons. The latter has now been observed in collisions with CO₂. Results are presented along with recent production efficiency measurements of Ps at high energies.