State-of-the-Art Predictions for C-parameter and a Determination of α[subscript s]

Abstract

The C-parameter event-shape distribution for e[superscript +]e[superscript −] annihilation into hadrons is computed in the framework of SCET including input from fixed-order perturbation theory. We calculate all missing ingredients for achieving N[superscript 3]LL resummation accuracy in the cross section, which is then matched onto O(α[superscript 3][subscript s]) fixed-order results. Hadronization power corrections are incorporated as a convolution with a nonperturbative shape function. Wide-angle soft radiation effects introduce an O(Λ[subscript QCD]) renormalon ambiguity in the cross section, which we cure by switching to the Rgap short-distance scheme. We also include hadron mass effects, but find their effect is rather small. Performing fits to the tail of the C-parameter distribution for many center of mass energies we find that the strong coupling constant is α[subscript s](m[subscript Z]) = 0.1121 ± 0.0015, with χ[superscript 2]/dof = 0.99.