Precise determination of α[subscript s] from the C-parameter distribution

Abstract

We present a global fit for α[subscript s](m[subscript Z]), 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 N[superscript 3]LL′ + O(α[3 over s]) + Ω[subscript 1] 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 Ω[subscript 1], which is defined in a scheme which eliminates the O(Λ[subscript QCD]) renormalon ambiguity. The resummation region plays a dominant role in the C-parameter spectrum, and in this region a fit for α[subscript s](m[subscript Z]) and Ω[subscript 1] is sufficient. We find α[subscript s](m[subscript Z]) = 0.1123 ± 0.0015 and Ω[subscript 1] = 0.421 ± 0.063 GeV with χ[superscript 2]/d.o.f. = 0.988 for 404 bins of data. These results agree with the prediction of universality for Ω[subscript 1] between thrust and C-parameter within 1-σ.