The mass of the W boson is determined in e(+)e(-) collisions at LEP by the
direct reconstruction of W decays in WW --> q (q) over barq (q) over bar an
d WW --> lvq (q) over bar events, supplemented by measurements using the ki
nematic properties of the leptons in the WW --> lvlv decay channel. The mai
n sample of W pairs is selected from an integrated luminosity of 174 pb(-1)
collected with the ALEPH detector in 1998 at a centre-of-mass energy of 18
8.63 GeV. The combined result from all channels is
m(W) = 80.432 +/- 0.072(stat.) +/- 0.041(syst.) +/- 0.019(FSI) +/- 0.017(LE
P) GeV/c(2),
where FSI represents the possible effects of final state interactions in th
e q (q) over barq (q) over bar channel. In a second two-parameter fit to th
e q (q) over barq (q) over bar, evq (q) over bar and mu vq (q) over bar cha
nnels, where the W mass and width are decoupled, the average W width is fou
nd to be 2.24 +/- 0.20(stat.) +/- 0.13(syst.) GeV/c(2), consistent with the
Standard Model prediction. The combination of the mass measurement present
ed in this paper together with those derived previously from the W pair cro
ss section at 161 and 172 GeV and direct reconstruction at 172 and 183 GeV
gives
m(W) = 80.418 +/- 0.061(stat.) +/- 0.040(syst.) +/- 0.019(FSI) +/- 0.017(LE
P) GeV/c(2).