Precise determination of α s from the C -parameter distribution

We present a global fit for αs (mZ), analyzing the available C -parameter data measured at center-of-mass energies between Q = 35 and 207 GeV. The experimental data is compared to a N3 LL' + $\mathscr{O}$ (α$3\atop{s}$) + Ω1 theoretical prediction (up to the missing four-loop cusp anomalous dimension), which includes power corrections coming from a field-theoretical nonperturbative soft function. The dominant hadronic parameter is its first moment Ω1, which is defined in a scheme which eliminates the $\mathscr{O}$ (ΛQCD) renormalon ambiguity. The resummation region plays a dominant role in the C -parameter spectrum, and in this region a fit for αs (mZ) and Ω1 is sufficient. We find αs (mZ) = 0.1123 ± 0.0015 and Ω1 = 0.421 ± 0.063 GeV with χ2/d . o . f . = 0.988 for 404 bins of data. These results agree with the prediction of universality for Ω1 between thrust and C -parameter within 1- σ .