Measurement of the W boson mass with the ALEPH detector

The W boson mass has been extracted using W-pairs decaying into e\nuqqbar and \mu\nuqqbar final states. The events were selected from the data collected with the ALEPH detector during th years 1998, 1999 and 2000, corresponding to a total integrated luminosity of about 650pb-1. A kinematic fit imposing four-momentum conservation is then applied to improve the invariant mass resolution. The W boson mass is obtained from the invariant mass spectrum by a Monte Carlo reweighting method. Since the statistical and systematical uncertainties are at the same level, the latter are investigated in great detail. The presented W boson mass in then included in a preliminary world average which is used to extract a upper limit on the Higgs boson mass.