Simultaneous projectile-target excitation in heavy ion collisions.

We calculate the lowest-order contribution to the cross section for simultaneous excitation of projectile and target nuclei in relativistic heavy ion collisions. This process is, to leading order, non-classical and adds incoherently to the well-studied semi-classical Weizsäcker-Williams cross section. While the leading contribution to the cross section is down by only 1/Z P from the semiclassical process, and consequently of potential importance for understanding data from light projectiles, we find that phase space considerations render the cross section utterly negligible.