Calculation of Higher Order Effects in Electron-Positron Pair Production   in Relativistic Heavy Ion Collisions
  We present a calculation of higher order effects for the impact parameter dependent probability for single and multiple electron-positron pairs in (peripheral) relativistic heavy ion collisions. Also total cross sections are given for SPS and RHIC energies. We make use of the expression derived recently by several groups where the summation of all higher orders can be done analytically in the high energy limit. An astonishing result is that the cross section, that is, integrating over all impact parameters, is found to be identical to the lowest-order Born result for symmetric collisions. For the probability itself on the other hand we find rather large effects at small impact parameters compared to the lowest order results, which translate to large effects for the cross section for multiple pair production. 
Kai Hencken (1), Dirk Trautmann (1) and Gerhard Baur (2), ((1) U   Basel, (2) FZ Juelich)