Measurement of the W boson mass and width in e+e- collisions at LEP

Abstract

The mass of the W boson is determined from the direct reconstruction of its decays into purely hadronic and semi-leptonic events in e+e- collisions at LEP. The data sample corresponds to an integrated luminosity of 683 inverse picobarns collected with the ALEPH detector at centre-of-mass energies up to 209 GeV. To minimise any effect from colour reconnection a new procedure is adopted in which low energy particles are not considered in the mass determination from the purely hadronic channel. The combined result from all channels is Mw = 80.440+-0.043(stat.)+-0.024(syst.)+-0.009(FSI)+-0.009(LEP) GeV/c**2 where FSI represents the possible effects of final state interactions in the purely hadronic channel. From two-parameter fits to the W mass and width, the W width is found to be Gw = 2.14+-0.09(stat.)+-0.04(syst.)+-0.05(FSI)+-0.01(LEP) GeV