Measurements of mass, width and gauge couplings of the W boson at LEP

We report on measurements of mass and total decay width of the W boson and of triple-gauge-boson couplings, γWW and ZWW, with the L3 detector at LEP. W-pair events produced in e+e− interactions between 161 GeV and 172GeV centre-of-mass energy are selected in a data sample corresponding to a total luminosity of 21.2 pb−1. The mass and total decay width of the W boson are determined to be MW = 80.75−0.27+0.26(exp.) ± 0.03 (LEP) GeV and ΓW = 1.74−0.78+0.88(stat.) ± 0.25(syst.)GeV, respectively. Limits on anomalous triple-gauge-boson couplings, γWW and ZWW, are determined, in particular −1.5 < δZ < 1.9 (95% CL), excluding vanishing ZWW coupling at more than 95% confidence level.