Non-resonant diagrams in radiative four-fermion processes

Abstract

The complete tree level cross section for e +e − → e − v eu dγ is computed and discussed in comparison with the cross sectionsfor e +e − → e − v eu d and e +e − → udu d . Event generators based on the GRACE package for the non-radiative and radiative case are presented. Special interest is brought to the effect of the non-resonant diagrams overlooked so far in other studies. Their contribution to the total cross section is presented for the LEP II energy range and for future linear colliders (√ s = 500 GeV). Effects, at the W pair threshold, of order 3% ( e − v eu d ) and 27% ( udu d ) are reported. Similar behaviour for the radiative case is shown. At √ s = 500 GeV, the relative contribution of the non-resonant diagrams for the radiative channel reaches 42.5%.