Precision measurement of the total cross section fore+e−→hadrons at a center-of-mass energy of 29 GeV

We report a high-precision measurement of the ratio R of the total cross section for $e^{+}$ $e^{\mathrm{-}}$→hadrons to that for $e^{+}$ $e^{\mathrm{-}}$→${\mu }^{+}$ ${\mu }^{\mathrm{-}}$, at a center-of-mass energy of 29.0 GeV using the MAC detector. The result is R=3.96±0.09. This value of R is used to determine a value of the strong coupling constant ${\alpha }_s$ of 0.23±0.06, nearly independent of fragmentation models. Two different analysis methods having quite different event-selection criteria have been used and the results are in agreement. Particular attention has been given to the study of systematic errors. New higher-order QED calculations are used for the luminosity determination and the acceptance for hadrons.