Strong coupling from e+e- →hadrons below charm

© 2018 authors. Published by the American Physical Society. We use a new compilation of the hadronic R-ratio from available data for the process e+e-→hadrons to determine the strong coupling, αs. We make use of all data for the R-ratio from threshold to a center-of-mass energy of 2 GeV by employing finite-energy sum rules. Data above 2 GeV, for which at present far fewer high-precision experimental data are available, do not provide much additional constraint but are fully consistent with the values for αs we obtain. Quoting our results at the τ mass to facilitate comparison to the results obtained from analogous analyses of hadronic τ-decay data, we find αs(mτ2)=0.298±0.016±0.006 in fixed-order perturbation theory, and αs(mτ2)=0.304±0.018±0.006 in contour-improved perturbation theory, where the first error is statistical, and the second error reflects our estimate of various systematic effects. These values are in good agreement with a recent determination from the OPAL and ALEPH data for hadronic τ decays.