| This thesis describes a measurement of the W boson mass from a fit to the transverse momentum spectrum of the muon in W decay. In past measurements this technique was used as a cross-check, however, now presents the best method in terms of systematic uncertainty. We discuss all sources of systematic uncertainty with emphasis on those to which the Muon pT measurement is particularly sensitive, specifically, those associated with modelling the production and decay of W bosons. The data were collected with the CDF II detector between March 2002 and September 2003 and correspond to an integrated luminosity of (191 +/- 11) pb-1. We measure the W mass to be (80.316 +/- 0.066stat. +/- 0.051syst.) GeV/c2 = (80.316 +/- 0.083) GeV/ c2. |