We report on the final electroweak measurements performed with data
taken at the Z resonance by the experiments operating at the
electron-positron colliders SLC and LEP. The data consist of 17 million
Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at
LEP, and 600 thousand Z decays by the SLID experiment using a polarised
beam at SLC. The measurements include cross-sections, forward-backward
asymmetries and polarised asymmetries. The mass and width of the Z
boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the
p parameter and the effective electroweak mixing angle for leptons, are
precisely measured:
m(Z) = 91.1875 +/- 0.0021 GeV,
Gamma(Z) = 2.4952 +/- 0.0023 GeV,
rho(l) = 1.0050 +/- 0.0010,
sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016.
The number of light neutrino species is determined to be 2.9840 +/-
0.0082, in agreement with the three observed generations of fundamental
fermions.
The results are compared to the predictions of the Standard Model (SM).
At the Z-pole, electroweak radiative corrections beyond the running of
the QED and QCD coupling constants are observed with a significance of
five standard deviations, and in agreement with the Standard Model. Of
the many Z-pole measurements, the forward-backward asymmetry in b-quark
production shows the largest difference with respect to its SM
expectation, at the level of 2.8 standard deviations.
Through radiative corrections evaluated in the framework of the Standard
Model, the Z-pole data are also used to predict the mass of the top
quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) =
80.363 +/- 0.032 GeV. These indirect constraints are compared to the
direct measurements, providing a stringent test of the SM. Using in
addition the direct measurements of m(t) and m(W), the mass of the as
yet unobserved SM Higgs boson is predicted with a relative uncertainty
of about 50% and found to be less than 285 GeV at 95% confidence
level. (c) 2006 Elsevier B.V. All rights reserved