An improved measuremebts of αS (MZ0) using energy correlations with the OPAL detector at LEP

We report on an improved measurement of the value of the strong coupling constant σs at the Z0 peak, using the asymmetry of the energy-energy correlation function. The analysis, based on second-order perturbation theory and a data sample of about 145000 multihadronic Z0 decays, yields αs(Mz0 = 0.118±0.001(stat.)±0.003(exp.syst.)−0.004+0.0009 (theor. syst.), where the theoretical systematic error accounts for uncertainties due to hadronization, the choice of the renormalization scale and unknown higher-order terms. We adjust the parameters of a second-order matrix element Monte Carlo followed by string hadronization to best describe the energy correlation and other hadronic Z0 decay data. The αs result obtained from this second-order Monte Carlo is found to be unreliable if values of the renormalization scale smaller than about 0.15 Ecm are used in the generator.