Non-linearities in estimators of trilinear gauge couplings that use total event rate

The total event rate of WW and single W production represents an important source of information on trilinear gauge couplings (TGC) at LEP 2. Present LEP analyses combine this information with the study of the four-fermion final-state angular distributions by means of an Extended Maximum Likelihood (EML) estimator. In general, it can be shown that the inclusion of total event rate induces non-linearities in the TGC estimators. In this letter, these biases are computed semi-analytically and calculations are carried out for typical LEP analyses at 161, 172 and 183 GeV.