Speaker
Description
We determine the strong coupling, $\alpha_s$, using finite-energy sum
rules and a new compilation of the hadronic $R$-ratio from available
data for $e^+e^- \to {\rm hadrons}$ below the charm threshold. Quoting our
final results at the tau mass to facilitate comparison to the results
of analyses of hadronic tau decay data, we find
$\alpha_s(m_\tau^2) = 0.298 \pm 0.017$ in fixed-order perturbation theory
and $\alpha_s(m_\tau^2) = 0.304 \pm 0.019$ in contour-improved
perturbation theory, where the quoted errors are largely dominated by
statistics. At the $Z$ boson mass, we find $\alpha_s(m_Z^2) = 0.1158 \pm 0.0022$
and $\alpha_s(m_Z^2) = 0.1166 \pm 0.025$, respectively. Our results are
in agreement with the world average and with recent extractions from
tau decay data. Our method provides an independent and competitive
strategy for the extraction of the strong coupling below the charm
threshold.
