A Precise Determination of alphas from the Heavy Jet Mass Distribution

A global fit for alphas(Mz) is performed on available e+e- data for the heavy jet mass distribution. The state-of-the-art theory prediction includes O(as^3) fixed-order results, N3LL' dijet resummation, N2LL Sudakov shoulder resummation, and a first-principles treatment of power corrections in the dijet region. Theoretical correlations are incorporated through a flat random-scan covariance matrix. The global fit results in 0.1145+0.0021-0.0019, compatible with similar determinations from thrust and C-parameter. Dijet resummation is essential for a robust fit, as it engenders insensitivity to the fit-range lower cutoff; without resummation the fit-range sensitivity is overwhelming. In addition, we find evidence for a negative power correction in the trijet region if and only if Sudakov shoulder resummation is included.