Abstract
We review recent theoretical efforts to explain observed similarities between electron-atom and positronium(Ps)-atom scattering which also extends to molecular targets. In the range of the projectile velocities above the threshold for Ps ionization (break-up) this similarity can be explained in terms of quasi-free electron scattering and impulse approximation. However, for lower Ps velocities more sophisticated methods should be developed. Our calculations of Ps scattering by heavy noble-gas atoms agree well with experiments at Ps velocities above the Ps ionization threshold. However, in contrast to electron scattering cross sections, at lower velocities they exhibit maxima whereas the experimental cross sections tend to decrease toward lower velocities indicating the same similarity with electron scattering cross section observed above the threshold. Our preliminary results for Ps-N2 scattering confirm experimental observation of a resonance similar to the ∏g resonance in electron-N2 scattering.
Highlights
Recent measurements [1, 2, 3, 4, 5] of positronium (Ps) collision cross sections for a number of atoms and small molecules show interesting similarities between the Ps scattering and the electron scattering in the intermediate energy range
To understand the physics of these similarities, we first have to identify the processes which contribute to the measured total cross sections for collisions of Ps with an atomic or molecular target A
The cross section for Ps ionization can be obtained by employing on-shell scattering amplitudes for electron-atom and positron-atom elastic scattering
Summary
Recent measurements [1, 2, 3, 4, 5] of positronium (Ps) collision cross sections for a number of atoms and small molecules show interesting similarities between the Ps scattering and the electron scattering in the intermediate energy range. Calculations of cross sections for Ps collisions with noble-gas atoms employing the impulse approximation show good agreement with experiment above the ionization threshold which corresponds to the Ps velocity 0.5 a.u. The cross section for Ps ionization can be obtained by employing on-shell scattering amplitudes for electron-atom and positron-atom elastic scattering This approach was successfully used for calculations of ionization of Ps in collisions with noble-gas atoms [9] and the hydrogen molecule [8], and the results are close to those of the more sophisticated impulse approximation [17].
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