Does theWmass reconstruction survive QCD effects?

In the hadronic decay mode of a pair of W bosons, ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$→${\mathit{W}}^{+}$ ${\mathit{W}}^{\mathrm{-}}$→${\mathit{q}}_1$q${\mathrm{¯}}_2$ ${\mathit{q}}_3$ ${\mathit{qbar}}_4$, QCD interference effects can mix up the two color singlets ${\mathit{q}}_1$q${\mathrm{¯}}_2$ and ${\mathit{q}}_3$q${\mathrm{¯}}_4$, i.e., produce hadrons that cannot be uniquely assigned to either of ${\mathit{W}}^{+}$ and ${\mathit{W}}^{\mathrm{-}}$. 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 40 MeV.