Measurement of the mass and width of the W boson in e+e− collisions at s=189 GeV

Abstract A measurement of the W 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 ν l q q ′ and W + W − → q q ′ q q′ 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 ′ q q′ channel, and LEP represents that arising from the knowledge of the beam energy of the accelerator. Combining this result with those 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 Γ W =2.266±0.176(stat)±0.056(syst)±0.052(FSI) GeV/ c 2 .