e+e− → e−veud from LEP to linear collider energies

The complete tree level cross-section for the process e+e− → e−veud is computed using the GRACE system, a program package for automatic amplitude calculation. Special attention is brought to the gauge violation problem induced by the finite width of the W-boson. The preserved gauge scheme is introduced and an event generator including double-resonant, single-resonant and non-resonant diagrams with no need for a cut on the electron polar angle is built. Below threshold, the single W and non-resonant diagrams give a substantial contribution to the total cross-section, at linear collider energies, the cross-section, for small electron polar angles, is simply dominated by these contributions. Since no cut needs to be applied to the electron, the generator can be used to estimate background for searches involving jets and missing energy. A monojet event rate estimation based on this process at LEP-I energy is discussed.