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We present a determination of the strong coupling constant from a fit of QCDpredictions for six event-shape variables, calculated atnext-to-next-to-leading order (NNLO) and matched to resummation in thenext-to-leading-logarithmic approximation (NLLA). These event shapes have beenmeasured in e+e- annihilations at LEP, where the data we use have beencollected by the ALEPH detector at centre-of-mass energies between 91 and 206GeV. Compared to purely fixed order NNLO fits, we observe that the central fitvalues are hardly affected, but the systematic uncertainty is larger becausethe NLLA part re-introduces relatively large uncertainties from scalevariations. By combining the results for six event-shape variables and eightcentre-of-mass energies, we find alpha_s(MZ)= 0.1224  +/- 0.0009 (stat)  +/- 0.0009 (exp)  +/- 0.0012 (had)  +/- 0.0035 (theo), which improves previously published measurements atNLO+NLLA. We also carry out a detailed investigation of hadronisationcorrections, using a large set of Monte Carlo generator predictions.

Determination of the strong coupling constant using matched NNLO+NLLA predictions for hadronic event shapes in e+e- annihilations