Single-W Production and Fermion-Loop Scheme: Numerical Results

The single-W production mechanism is synonymous to the electron-positron annihilation into electron, neutrino and a W boson with the outgoing electron lost in a small cone around the beam direction. It requires a Renormalization Scheme that preserves gauge invariance and fermion masses cannot be neglected in the calculation. A recently proposed generalization of the so-called Fermion-Loop scheme is applied to the evaluation of observables at LEP 2 energies. Single-W processes are dominated by a regime of low momentum transfer of the outgoing electron and any high-energy Renormalization Scheme fails to give the correct description of the scale. The Fermion-Loop scheme automatically converts all couplings of the theory into couplings that are running at the appropriate scale. Therefore, in addition to represent the only scheme fully justified on a field-theoretical basis, the Fermion-Loop is the best starting point to include radiative corrections into single-W production. Numerical results are presented, showing a decrease in the predictions that can be sizeable. There is no naive and overall rescaling of the e.m. coupling constant, in any pragmatic scheme, that can reproduce the Fermion-Loop results, at the requested accuracy, for all configurations and for all kinematical cuts.