Application of “optimised” perturbation theory to determination of αs(MZ2) from hadronic event shape observables in e+e− annihilation☆

Abstract We have applied so-called “optimised” perturbation theory to resolve the renormalisation-scale (μ) ambiguity of exact O( α s 2 ) QCD calculations of event shape observables in e + e − → hadrons. We fitted the optimised predictions for 15 observables to hadronic Z 0 decay data from the SLD experiment to determine α s ( M Z 2 ). Comparing with results using the physical scale μ = Mz we found no reduction in the scatter among α s ( M Z 2 ) values from the 15 observables, implying that the O( α s 2 ) predictions with optimised scales are numerically no closer to the exact all-orders results than those with the physical scale.