Positron scattering from Mg atoms

Scattering of low-energy positrons from Mg atoms is considered using many-body theory methods. For the first time the contribution of the Ps-formation channel is taken into account in addition to the polarization potential of the atom. At low energies the virtual Ps formation creates a strong attraction in the positron-atom channel, which produces positron-atom bound states in the s and p waves (0.985 and 0.159 eV are the corresponding binding energies), and a low-lying d-wave resonance at 1 eV. At higher energies this contribution gives rise to an effective positron-atom repulsion. On the whole, the inclusion of the Ps-formation contribution drastically changes the behaviour of the phase shifts and the shape of the partial-wave cross sections below 20 eV. Total and inelastic positron-Mg cross sections have been calculated. It appears that the present theory can explain the very recent results of the first experiment on positron-Mg scattering.