HIGH-ENERGY APPROXIMATION FOR ON-SHELL W-PAIR PRODUCTION

Starting from the exact virtual and soft-photonic O(alpha) corrections to the differential cross section for on-shell W-pair production we d erive a high-energy approximation valid for energies much higher than the W-boson mass. This approximation is improved by taking into accoun t extra terms for large top-quark and Higgs-boson masses as well as th e exact results for the leading low-energy universal corrections assoc iated with the running of alpha and the rho-parameter. For 90-degrees scattering angle and in those situations where the cross section is la rge, this approximation reproduces the full virtual and soft-photonic O(alpha) result to better than approximately 1% for energies above 500 GeV. In the angular range -0.9 < costheta < 0.9 it is better than 1% for energies above 1-3 TeV, depending on the polarization.