A combination by the LEP QCD Working Group of αs values derived from event shape variables at LEP

The LEP QCD Working Group has produced a combination of αs values derived from event-shape distributions. The distributions are measured at scales below the mass of the Z boson up to 206 GeV. Values of αs are all extracted using the consistent application of O(αs2)+ NLLA predictions with the modified Log(R) matching scheme. A combined αs is obtained for each experiment and observable using at least two experiments in each case for energies above at ad above the mass of the Z boson. A consistent treatment and controlled breakdown is made of the sources of uncertainty on the input values. The combined best value for αs(MZ) 0.11 ± 0.003 ± 0.003. The dominant uncertainty is theoretical, due to the effects of missing higher order contributions