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

A. D. Martin·J. Outhwaite·M. G. Ryskin
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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.

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A. D. Martin, J. Outhwaite, M. G. Ryskin. 2001-02-12. Improving alpha_QED(M_Z^2) and the charm mass by analytic continuation. https://doi.org/10.1007/s100520100598

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