Higher-order pair-conversion peaks in heavy-ion collisions

We analyze quantum electrodynamic pair creation from vibrating nuclear quasimolecules which may occur in collisions of heavy ions. We find that higher-order processes, which can be phenomenologically relevant for sufficiently long lived systems, can result in coincident narrow peaks even for subcritical systems. The Z dependence of the energy of the peaks can be much softer than that predicted for positrons from sparking of the vacuum. Our results may be relevant to peaks which have been observed at the Gesellschaft für Schwerionenforschung (GSI).