Direct Measurement of the $W$ Boson Width

We present a direct measurement of the $W$ boson width using 370 $pb^{-1}$ and 330 $pb^{-1}$ of data collected with the CDF II detector for the electron and muon decay channels respectively. The measurement is made by fitting to the tail of the transverse mass distribution, exploiting the slower fall-off of the Breit Wigner width component compared to the Gaussian resolution component.