Determination of αs and heavy-quark masses from recent measurements of R( s)

Abstract

In this paper we compare recent experimental data for the total cross section σ( e + e −→hadrons) with the up-to-date theoretical prediction of perturbative QCD for those energies where perturbation theory is reliable. The excellent agreement suggests the determination of the strong coupling α s from the measurements in the continuum. The precise data from the charm threshold region, when combined with the recent evaluation of moments with three loop accurracy, lead to a direct determination of the short distance MS charm quark mass. Our result for the strong coupling constant α s (4) (5 GeV)=0.235 +0.047 −0.047 corresponds to α s (5)( M Z )=0.124 +0.011 −0.014, for the charmed quark mass we find m c ( m c )=1.304(27). Applying the same approach to the bottom quark we obtain m b ( m b )=4.209(50) GeV. Whereas our result for α s ( M Z ) serves as a useful cross check for other more precise determinations, our values for the charm and bottom quark masses are more accurate than other recent analyses.