Pair production and bremsstrahlung contributions to the stopping of relativistic heavy ions

We examine the energy loss to electron-positron pairs and bremsstrahlung for relativistic heavy ions penetrating matter. Pair production is the dominant source of loss at extreme projectile energies, and already at energies of a few hundred GeV/u it may add several per cent to the stopping power. An analytical formula for the pair-production contribution to the average energy loss is produced. In bremsstrahlung coherent action of the constituents of each collision partner is required in order to keep the nuclei from breaking up. This limits the emission substantially at high energies compared to the emission in collisions between pointlike non-composite but otherwise similar objects. A simple formula for the bremsstrahlung loss is presented. We conclude with remarks on the statistics of the energy-loss processes.