Abstract
We have measured the total normalized cross section R for the process e +e − → hadrons at centre-of-mass energies between 14.0 and 46.8 GeV based on an integrated luminosity of 60.3 pb −1. The data are well described by the standard SU(3) c⊗SU(2) L⊗U(1) model with the production of the five known quarks. No open production of a sixth quark with charge 2/3 or 1/3 occurs below a centre-of-mass energy of 46.6 or 46.3 GeV, respectively. A fitting procedure which takes the correlations between measurements into account was used to determine the electroweak mixing angle sin 2θ w and the strong coupling constant α s( S) in second-order QCD. We applied this procedure to the CELLO data and in addition included the data from other experiments at PETRA and PEP. Both fits give consistent results. The fit to the combined data yields α s (34 2 GeV 2) = 0.165±0.030, and sin 2 θ w = 0.236±0.020. Fixing sin 2θ w at the world average value of 0.23 yields α s (34 2 GeV 2) = 0.169±0.025.
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