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 = 18
9 GeV with the OPAL detector, The invariant mass distributions from 970 W+W
- --> qqqq and 1118 W+W- --> qq(l)v(l) candidate events are used to measure
the mass of the W boson, M-W = 80.451 +/- 0.076 (stat.) +/- 0.049 (syst.)
GeV, A direct measurement of the width of the W boson gives Gamma (W) = 2.0
9 +/- 0.18 (stat,) +/- 0.09 (syst,) GeV, The results are combined with prev
ious OPAL results from 78 pb(-1) of data recorded with roots from 161 to 18
3 GeV, to obtain: M-W = 80.432 +/- 0.066 (stat,) +/- 0.035 (syst,) GeV, Gam
ma (W) = 2.04 +/- 0,16 (stat,) +/- 0.09 (syst.) GeV, The consistency of the
direct measurement of Mw with that inferred from other measurements of ele
ctroweak parameters provides an important test of the Standard Model of ele
ctroweak interactions. (C) 2001 Elsevier Science B,V, All rights reserved.