Measurement of the Mass and Width of the W Boson in e+e- Collisions at 189 GeV

Abstract

The mass and width of the W boson are determined in e+e- collisions at LEP using 183 pb^-1 of data recorded at a centre-of-mass energy roots=189 GeV with the OPAL detector. The invariant mass distributions from 970 WW->qqqq and 1118 WW->qqln candidate events are used to measure the mass of the W boson, Mw = 80.451 +- 0.076(stat.) +- 0.049(syst.) GeV. A direct measurement of the width of the W boson gives Gw=2.09 +- 0.18(stat.) +- 0.09(syst.) GeV. The results are combined with previous OPAL results from 78 pb^-1 of data recorded with roots from 161 to 183 GeV, to obtain: Mw = 80.432 +- 0.066(stat.) +- 0.045(syst.) GeV, Gw = 2.04 +- 0.16(stat.) +- 0.09(syst.) GeV. The consistency of the direct measurement of Mw with that inferred from other measurements of electroweak parameters provides an important test of the Standard Model of electroweak interactions.