Tests of QCD at LEP

Abstract

Recent results on tests of perturbative QCD in hadronic final states of Z 0 bosons are reviewed. Studies of 3- and 4-jet final states provide significant tests of the basic quantum numbers of the theory, as the gluon spin and the number of colours ( N c = 3). The energy dependence of jet production rates provides direct evidence for asymptotic freedom and for the nonabelian nature of QCD. The strong coupling α s is determined, from studies of event topologies and jet production rates, to be α s ( M Z 0 ) = 0.115 ± 0.008 in second order perturbation theory, where the error is dominated by the unknown contribution of higher orders. Combined analyses of Z 0 line shapes and decay asymmetries lead to α s ( M Z 0 ) = 0.131 ± 0.011, which is limited by data statistics. The weighted average is α s ( M Z 0 ) = 0.120 ± 0.006. Studies of soft hadron and gluon coherence phenomena are shortly reviewed.