A Precise Determination of ${\alpha }_s$ from the Heavy Jet Mass Distribution

A global fit for ${\alpha }_s(m_Z)$ is performed on available $e^{+}{e}^{-}$ data for the heavy jet mass distribution. The state-of-the-art theory prediction includes $\mathcal{O}({\alpha }_s^3)$ fixed-order results, N${}^3$LL${}^{\mathrm{\prime }}$ dijet resummation, N${}^2$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 $0.1148_{-0.0022}^{+0.0015}$, 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.