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 N3LL′ +
O(αs3) + Ω1 theoretical prediction (up to the
missing 4-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 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±0.063GeV with
χ2/dof=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.Comment: 24 pages, 19 figure