Lower Bound on the Intermediate-Boson Mass

We report a search for the $W$ boson via the production process ${\nu }_{\mu }+Z\to W^{+}+{\mu }^{-}+Z$ and decay process $W^{+}\to {\mu }^{+}+{\nu }_{\mu }$. We have set a firm lower bound on the mass of the $W$ boson as a function of the branching fraction into leptons [$B=\frac{(W\to l+\nu )}{(W\to \mathrm{all})}$]. For example, we have determined that $M_W>4.4\mathrm{}$ GeV/${\mathit{c}}^2$ (90% confidence limit) for $B=0.5\mathrm{}$.