Measurement of alpha_s in radiative hadronic events at OPAL

Abstract

Hadronic final states with a hard isolated photon are studied using data taken at centre-of-mass energies around $\Mz$ with the OPAL detector at LEP. The strong coupling $\as$ is extracted by fitting event shape variables for the reduced centre-of-mass energies ranging from 20 GeV to 80 GeV, and the energy dependence of $\as$ is studied. Combining all the values using different event shape variables and energies gives: \asmz=0.1176\pm 0.0012(stat.)^{+0.0093}_{-0.0085}(syst.).