Non-resonant diagrams in radiative four-fermion processes

Abstract

The complete tree level cross section for $e^{+}{e}^{-}\to e^{-}\bar{\hat{I}}{½}_{e}u\bar{d}{\hat{I}}^3$ is computed and discussed in comparison with the cross sections for $e^{+}{e}^{-}\to e^{-}\bar{\hat{I}}{½}_{e}u\bar{d}$ and $e^{+}{e}^{-}\to \bar{u}du\bar{d}$. 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 ($\sqrt{s}$ =500 GeV). Effects, at the W pair threshold, of order 3\% ($e^{-}\bar{\hat{I}}{½}_{e}u\bar{d}$) and 27\% ($\bar{u}du\bar{d}$) are reported. Similar behaviour for the radiative case is shown. At $\sqrt{s}$ = 500 GeV, the relative contribution of the non-resonant diagrams for the radiative channel reaches 42.5\%.

6 pages, latex, KEK-CP-015, KEK Preprint 94-46, LAPP-Exp.-94.09