This Letter describes a direct measurement of the $W$ boson total decay width, ${\Gamma }_W$, using the Collider Detector at Fermilab. The measurement uses an integrated luminosity of $90{\mathrm{pb}}^{-1\mathrm{}}$, collected during the 1994–1995 run of the Fermilab Tevatron $p\overline{p}$ collider. The width is determined by normalizing predicted signal and background distributions to 49 844 $W\to e\nu$ candidates and 21 806 $W\to \mu \nu$ candidates in the transverse-mass region $M_T<200\mathrm{}$ GeV and then fitting the predicted shape to the 438 electron events and 196 muon events in the high- $M_T$ region, $100<\mathrm{}{M}_T<200\mathrm{}$ GeV. The result is ${\Gamma }_W=2.04\mathrm{}\pm 0.11\left(\mathrm{stat}\right)\pm 0.09\left(\mathrm{syst}\right)\mathrm{GeV}$.

• Received 17 April 2000

DOI:https://doi.org/10.1103/PhysRevLett.85.3347