Measurement of the mass and width of the W boson in e(+)e(-) collisions at root s=189 GeV

A measurement of the FV mass and width has been performed by the DELPHI Collaboration using the data collected during 1998. The data sample has an integrated luminosity of 155 pb(-1) and an average centre-of-mass energy of 188.6 GeV. Results are obtained by applying the method of direct reconstruction of the mass of the W from its decay products in both the W+W- → l (v) over bar (l)q (q) over bar ' and W+W- → q (q) over bar '(q) over barq ' channels. The W mass result for the 1998 data set is M-W = 80.387 +/- 0.087(stat) +/- 0.034(syst) +/- 0.017(LEP) +/- 0.035(FSI) GeV/c(2), where FSI represents the uncertainty due to final state interaction effects in the q (q) over bar 'q (q) over bar ' channel, and LEP represents that arising from the knowledge of the beam energy of the accelerator Combining this result with Ghost: previously published by the DELPHI Collaboration gives the result M-W = 80.359 +/- 0.074(stat) +/- 0.032(syst) +/- 0.017(LEP) +/- 0.033(FSI) GeV/c(2). The combined value for the W width is Gamma (W) = 2.266 +/- 0.176(stat) +/- 0.056(syst) +/- 0.052(FSI) GeV/c(2).