A study of QCD structure constants and a measurement of\(\alpha _s (M_{Z^0 } )\) at LEP using event shape observables

The dependence of event shape cross sections on the QCD structure constantsC A ,C F andT F is studied using data from the OPAL detector at LEP. The observables Thrust, Heavy Jet Mass, Total and Wide Jet Broadening are used. They allow the use ofO(α s 2 ), resummed NLLA, and combinedO(α s 2 ) plus resummed NLLA QCD calculations so that a comparison between the different approaches can be performed. The measured values of the structure constants are found to be consistent with standard QCD based on SU(3) and five active quark flavours. A measurement of the strong coupling constant using NLLA QCD calculations alone results in\(\alpha _s (M_{Z^0 } ) = 0.113_{ - 0.008}^{ + 0.009}\), which complements our previous determinations.