Low-energy antinucleon-nucleus interaction revisited

Annihilation cross sections of antiprotons and antineutrons on the proton between 50 and 400 MeV/c show Coulomb focusing below 200 MeV/c and almost no charge-dependence above 200 MeV/c. Similar comparisons for heavier targets are not possible for lack of overlap between nuclear targets studied with p̄ and n̄ beams. Interpolating between p̄-nucleus annihilation cross sections with the help of an optical potential to compare with n̄-nucleus annihilation cross sections reveal unexpected features of Coulomb interactions in the latter. Direct comparisons between n̄-nucleus and p̄-nucleus annihilations at very low energies could be possible if p̄ cross sections are measured on the same targets and at the same energies as the available cross sections for n̄. Such measurements may be feasible in the foreseeable future.