Determination of αs from hadronic event shapes in e+e− annihilation at 192⩽s⩽208 GeV

Abstract Results are presented from a study of the structure of high energy hadronic events recorded by the L3 detector at s ⩾192  GeV. The distributions of several event shape variables are compared to resummed O (α s 2 ) QCD calculations. We determine the strong coupling constant at three average centre-of-mass energies: 194.4, 200.2 and 206.2 GeV. These measurements, combined with previous L3 measurements at lower energies, demonstrate the running of α s as expected in QCD and yield α s ( m Z )=0.1227±0.0012±0.0058, where the first uncertainty is experimental and the second is theoretical.