DOES THE W-MASS RECONSTRUCTION SURVIVE QCD EFFECTS

In the hadronic decay mode of a pair of W bosons, e+e- --> W+W- --> q1 q2q3q4BAR, QCD interference effects can mix up the two color singlets q1q2BAR and q3q4BAR, i.e., produce hadrons that cannot be uniquely ass igned to either of W+ and W-. We show that interference is negligible for energetic perturbative gluon emission, and develop models to help us to estimate the nonperturbative effects. The total contribution to the systematic error on the W mass reconstruction may be as large as 4 0 MeV.