Determination of the W mass from semileptonic W decays

The W mass is a fundamental parameter of the Standard Model. In comparison with the indirect measurement from precise electroweak results at lower energies, the W mass provides an important test of the Standard Model. In combination with the top mass a prediction for the Higgs boson mass is possible. From data corresponding to an integrated luminosity of 153.8 pb-1 taken during the 189 GeV run in 1998 by the DELPHI experiment, the W mass from direct reconstruction has been determined using semileptonic W decays. The event selection is based on an iterative discriminant analysis and the mass was determined using a two dimensional likelihood method. The combined value obtained from all semileptonic decay channels is mW(WW → l anti νqq) = 80.059 GeV ± 157 MeV (stat) ± 49 MeV (syst). (orig.)