A GLOBAL DETERMINATION OF ALPHA(S)(M(Z)0) AT LEP

The value of the strong coupling constant, alpha(s)(M(Z)0), is determined from a study of 15 different observables in hadronic Z0 and tau-decays. The study includes global event shape variables, jet production rates, energy correlations, the Z0 line shape and decay asymmetries and the hadronic branching fraction of tau-leptons. Differences between the alpha(s) values from the different observables can be consistently attributed to unknown higher order contributions to the O(alpha(s)2) calculations. These uncertainties may be parametrized by variations of the renormalization scale and of the parton virtuality to which the data are corrected, separately for each observable, resulting in a consistent description of the event shapes, jet rates and energy correlations with the value alpha(s)(M(Z)0)=0.122(-0.005)+0.006) in O(alpha(s)2). The error is dominated by the theoretical uncertainties. Application of recent calculations which include the resummation of leading and next-to-leading logarithms to all orders for some observables confirm this result with a reduced sensitivity to renormalization scale variations. The Z0 line shapes and tau-lepton branching ratios yield alpha(s)(M(Z)0)=0.148 +/-0.021 and alpha(s)(M(Z)0)=0.123(-0.007)+0.006, respectively, in O(alpha(s)3). These measurements and their uncertainties are entirely independent of each other and from event shape and jet observables; the good agreement of the resulting alpha(s) values thus constitutes an important consistency check of the reliability of perturbative QCD.