DETERMINATION OF ALPHA-S IN 2ND-ORDER QCD FROM HADRONIC-Z DECAYS

Distributions of event shape variables obtained from 120600 hadronic Z decays measured with the DELPHI detector are compared to the predictions of QCD based event generators. Values of the strong coupling constant alpha(s) are derived as a function of the renormalization scale from a quantitative analysis of eight hadronic distributions. The final result, alpha(s) (M(Z)) = 0.113 +/- 0.007, is based on second order perturbation theory and uses two hadronization corrections, one computed with a parton shower model and the other with a QCD matrix element model.