The Influence of the Experimental Methodology on the QED Theoretical Uncertainties on the Measurement of MW at LEP

Previous studies of the QED systematic uncertainties on the LEP measurement of the W-boson mass, MW, have used idealized event selections and fitting procedures. In this paper, the Monte Carlo tandem of KoralW and YFSWW is used to investigate how the full experimental MW extraction procedure affects these estimates. It is found that the kinematic fitting used in the experimental determination of MW enhances the sensitivity to QED corrections involving real photon production. It is concluded that the previous estimates of the QED theoretical uncertainty on the LEP2 MW measurement may be too small. A simple procedure for approximating the effect of the kinematic fit at the level of the generated four fermions is proposed. This procedure would allow previous theoretical studies to be repeated using a much closer approximation of the real experimental mass extraction method. Finally, the possibility of setting experimental limits on O(α) theoretical uncertainties using identified ee → WWγ events is discussed.