Final αs combinations from the LEP QCD Working Group

The LEP QCD Working Group has for several years produced combinations of αs values derived from eventshape 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 final combinations are now being performed, with the last of the definitive inpits being received for the Summer 2004 conferences The combined best value for LEP I is αs(MZ) = 0.1202 ± 0.0006(expt.) ± 0.0050(theo.) and for LEP II is α.(MZ) = 0.1202 ± 0.0011(expt.) ± 0.0046(theo.). The dominant theoretical uncertainty is due to the effects of missing higher order contributions in the perturbative predictions used.