alpha_s and the tau hadronic width

Abstract

Different choices exist for the renormalisation group resummation in the determination of ${\alpha }_s$ from hadronic $\tau$ decays: namely fixed-order (FOPT) and contour-improved perturbation theory (CIPT). The two approaches lead to systematic differences in the resulting ${\alpha }_s$. On the basis of a model for higher-order terms in the perturbative series, which incorporates well-known structure from renormalons, it is found that while CIPT is unable to account for the fully resummed series, FOPT smoothly approaches the Borel sum. Employing the model to determine ${\alpha }_s$ yields ${\alpha }_s(M_{\tau })=0.316\pm 0.006$, which after evolution leads to ${\alpha }_s(M_Z)=0.1180\pm 0.0008$.

Comments: 6 pages, 2 figures. Talk given at the 10th International Workshop on Tau Lepton Physics, Novosibirsk, Russia, Sep. 22-25, 2008