Charmonium decays: J/psi --> e+e- and etac --> gamma gamma
Abstract
We compute the O(alphas2) correction to the decay rate etac --> gamma gamma and discuss its implications for precision quarkonium physics. We study the suitability of the ratio Gamma(J/psi --> e+e-)/Gamma(etac --> gamma gamma), in which the non-perturbative or soft effects cancel at O(alphas0,1), for extracting fundamental parameters of QCD at low energies. We show that the QCD-based theory of charmonia is not capable of predicting this ratio with any degree of confidence.
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