Lepton identification criteria and performances for W selections

The criteria used to identify electrons and muons from W decays in the leptonic event selections are reviewed. The procedures to recalibrate the electron estimators are also described. Data and Monte Carlo performances of such identification criteria are studied using dilepton events at the Z peak, and at LEP2 energies, as a function of the polar angle of the lepton. Correction factors for the W selections are then evaluated by convoluting the differences measured at the Z peak with the angular spectrum of the selected leptons from W decays. The uncertainty due to the momentum dependence of the measured efficiencies is evaluated through the results obtained with high energy dileptons. The final results for the W lepton-id correction and systematic uncertainty for W-pair analyses are on average: Delta eff(e)= -0.5+-0.2+-0.6% Delta eff(mu)= +-0.0+-0.1+-0.4% where the fist error comes from the Z peak analysis and the second error from the differences observed at higher energies.