State-of-the-Art Predictions for C-parameter and a Determination of αs

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 (NLL)-L-3 resummation accuracy in the cross section, which is then matched onto O(alpha(3)(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(Lambda(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 alpha(s)(m(Z)) = 0.1123 +/- 0.0015, with chi(2)/dof = 0.99.