ELECTROMAGNETIC ELECTRON-POSITRON PAIR PRODUCTION IN HEAVY-ION COLLISIONS WITH IMPACT PARAMETER ZERO

We present a calculation of the second-order process of electron-posit ron pair creation by the electromagnetic fields of two relativistic he avy ions for impact parameter b zero. Total probabilities as well as d ifferential ones are presented. A comparison with the results of the d ouble equivalent-photon approximation (DEPA) shows explicitly the inap plicability of this approximation in the case of total probabilities. We discuss the creation of pairs with large invariant mass. The DEPA r esults are too high, which can be traced back to the mass singularity of the photon cross section at very small angles, giving a discrepancy , whereas the agreement between our result and DEPA is good for larger angles.