State-of-the-art predictions for C-parameter and a determination of α s

The C-parameter event-shape distribution for e + e − annihilation into hadrons is computed in the framework of SCET including input from fixed-order perturbation theory. We calculate all missing ingredients for achieving N3LL resummation accuracy in the cross section, which is then matched onto O(α3) fixed-order results. Hadronization power corrections are incorporated as a convolution with a nonperturbative shape function. Wide-angle soft radiation effects introduce an O ( α s 3 ) 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 s (m Z ) = 0.1123±0.0015, with χ 2 /dof = 0.99.