Achard, P (reprint author), Univ Michigan, Ann Arbor, MI 48109 USA.
The cross section of W-boson pair-production is measured with the L3 detector at LEP. In a data sample corresponding to a total luminosity of 629.4 pb(-1), collected at centre-of-mass energies ranging from 189 to 209 GeV, 9834 four-fermion events with W bosons decaying into hadrons or leptons are selected. The total cross section is measured with a precision of 1.4% and agrees with the Standard Model expectation. Assuming charged-lepton universality, the branching fraction for hadronic W-boson decays is measured to be: Br(W --> hadrons) = 67.50 +/- 0.42(stat.) +/- 0.30(syst.)%, in agreement with the Standard Model. Differential cross sections as a function of the W- production angle are also measured for the semi-leptonic channels qqev and qqmuv. (C) 2004 Published by Elsevier B.V.