Measurement of the W Mass from LEP2

Abstract

In 1997 each LEP experiment collected approximately $55 {pb}^{-1}$ of data at a center-of-mass energy of 183 GeV. These data yield a sample of candidate $e^+e^- \to W^+W^-$ events from which the mass of the W boson, M_W, is measured. The preliminary LEP combined result, including data taken at $\roots = 161$ and 172 GeV and assuming the Standard Model relation between the W decay width and mass, is $M_W = 80.38 \pm 0.07 (exp) \pm 0.03 (CR/BE) \pm 0.02 (E_{bm})$ GeV, where the uncertainties correspond to experimental, colour-reconnection/Bose-Einstein, and LEP beam energy respectively.