Improving alpha_QED(M_Z^2) and the charm mass by analytic continuation

Abstract

The standard determination of the QED coupling on the Z pole is performed using the latest available data for R. The direct application of analytic continuation techniques is found not to improve the accuracy of the value of α(M_Z^2). However they help to resolve an ambiguity in the values of R in the energy region \sqrt{s} < 2 GeV, which, in turn, reduces the uncertainty in α(M_Z^2). Moreover, they provide a sensitive determination of the mass of the charm quark. The favoured solution, which uses the inclusive data for R for \sqrt{s} < 2 GeV, has a pole mass m_c = 1.33-1.40 GeV and α^{-1}(M_Z^2) = 128.972 +/- 0.026; whereas if the sum of the exclusive channels is used to determine R in this region, we find α^{-1}(M_Z^2) = 128.941 +/- 0.029.