BHABHA SCATTERING AT HIGH-ENERGY

We show how to use the results of first-order (one-loop) perturbation theory to build a nonperturbative description of realistic high-energy Bhabha scattering, for a wide range of experimental cuts and both large and small scattering angles, with 1% estimated precision. Correspondingly, an event generator BHA-GEN is implemented. The resulting values of the cross-section are compared with those of the other programs existing in the literature, which are also mainly based on the same one-loop results. The agreement, after accounting the different kinematical cuts, is in general within 1%. We stress that, to improve the theoretical accuracy, a complete understanding of the different implementations of the nonperturbative effects based on one-loop corrections is necessary; we also emphasize that a correct definition of the events is an essential point of the accurate description of the process, accounting by itself for a few per cent difference. Only after settling those problems one can meaningfully consider the two-loop corrections, which are anyhow needed to push the theoretical precision below the 1% level.