Abstract
Submitted to Phys. Rev. Lett. July 6, 2007.; We present a measurement of the W boson mass using 200 pb-1 of data collected in p anti-p collisions at s**(1/2) = 1.96 TeV by the CDF II detector at Run II of the Fermilab Tevatron. With a sample of 63964 W --> e nu candidates and 51128 W --> mu nu candidates, we measure M_W = (80413 +/- 34_stat +/- 34_syst = 80413 +/- 48) MeV/c2. This is the most precise single measurement of the W boson mass to date.