Collisions of H and ¯H

Abstract

Theoretical studies of the collisions of the atoms of hydrogen and antihydrogen at ultracold temperatures are summarised. Rearrangement may occur leading to the formation of protonium and positronium. The most probable channel yields positronium in its ground 1s state and protonium in the state with principal quantum number N = 24. The elastic cross section resulting from scattering in the Born Oppenheimer H¯H potential is calculated. It is crossed by the rearrangement cross section, which is increasing inversely as the velocity, at an energy of about 2 × 10 ⁻⁷ atomic units. It appears that sympathetic cooling down to perhaps 0.1K may be possible before it is overtaken by annihilation. It is pointed out that the quasi-molecule H¯H has an electric dipole moment so that radiation is produced during the collision process and may serve as a diagnostic probe of the event.