2018 Impact factor 4.843
Particles and Fields
Eur. Phys. J. C 17, 241-261
DOI 10.1007/s100520000485

Measurement of the W mass and width
in e+e- collisions at 189GeV

The ALEPH Collaboration

R. Barate - et al.

Laboratoire de Physique des Particules (LAPP), IN2P3-CNRS, 74019 Annecy-le-Vieux Cedex, France

Received: 15 March 2000 / Published online: 8 September 2000 - © Springer-Verlag 2000

The mass of the W boson is determined in e+e- collisions at LEP by the direct reconstruction of W decays in $\mathrm{W}\mathrm{W}\rightarrow\mathrm{q\bar{q}}\mathrm{q\bar{q}}$ and $\mathrm{W}\mathrm{W}\rightarrow\mbox{$\ell\nu \mathrm{q\bar{q}}$ }$ events, supplemented by measurements using the kinematic properties of the leptons in the $\mathrm{W}\mathrm{W}\rightarrow\mbox{$\ell\nu $ }\mbox{$\ell\nu $ }$ decay channel. The main 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 188.63GeV. The combined result from all channels is

\begin{displaymath}m_\mathrm{W} = 80.432
\pm 0.072{\mathrm{(stat.)}}
\pm 0.041...
\pm 0.017{\mathrm{(LEP)}}~\mathrm{GeV}/c^2,

where FSI represents the possible effects of final state interactions in the $\mathrm{q\bar{q}}\mathrm{q\bar{q}}$ channel. In a second two-parameter fit to the $\mathrm{q\bar{q}}\mathrm{q\bar{q}}$, $\mathrm{e}\nu \mathrm{q\bar{q}}$ and $\mu\nu \mathrm{q\bar{q}}$ channels, where the W mass and width are decoupled, the average W width is found to be $2.24 \pm 0.20{\mathrm{(stat.)}} \pm
0.13{\mathrm{(syst.)}}$GeV/c2, consistent with the Standard Model prediction. The combination of the mass measurement presented in this paper together with those derived previously from the W pair cross section at 161 and 172GeV and direct reconstruction at 172 and 183GeV gives

\begin{displaymath}m_\mathrm{W} = 80.418
\pm 0.061{\mathrm{(stat.)}}
\pm 0.040...
\pm 0.017{\mathrm{(LEP)}}~\mathrm{GeV}/c^2.\end{displaymath}

Copyright Società Italiana di Fisica, Springer-Verlag 2000