A precise determination of $\alpha_s$ from the heavy jet mass distribution

A global fit for \\alpha_s(m_Z) α s ( m Z ) is performed on available e^+e^- e + e − data for the heavy jet mass distribution. The state-of-the-art theory prediction includes NNLO fixed-order results, N ^3 3 LL ^\\prime ′ dijet resummation, N ^2 2 LL 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 0.1148^{+ 0.0015}_{-0.0022} 0.1148 − 0.0022 + 0.0015 , compatible with similar determinations from thrust and C 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.