Event shape distributions and αs determination

We use a factorization formula for thrust and heavy jet mass distributions based on soft-collinear effective theory. The result is applicable in the peak, tail, and far-tail regions. The formula includes three-loop fixed-order QCD results, resummation of singular partonic terms with NNNLL accuracy and hadronization effects from fitting a universal nonperturbative soft function defined in field theory. We do not rely on Monte Carlo generators to determine nonperturbative effects since they are not compatible with higher order perturbative analyses. We use our theoretical expressions to fit for as and the leading power correction in thrust and heavy jet mass tail distributions, and also to moments of the thrust distribution. Our determination is one of the world's most precise extractions of αs. (author)