Bound-bound pair production in relativistic collisions

Electron-positron pair production is considered in the relativistic collision of a nucleus and an anti-nucleus, in which both leptons are created in bound states of the corresponding nucleus-lepton system. Compared to free and bound-free pair production, this process is shown to display a qualitatively different dependency both on the impact energy and on the charges of the colliding particles. Interestingly, at high impact energies the cross section for this process is found to be larger (due to a bigger statistical weight) than that for the analogous atomic process of non-radiative electron capture, although the latter does not involve the creation of new particles.