Charmonium decays: J/psi --> e+e- and eta_c --> gamma gamma

Abstract

We compute the O(alpha_s^2) correction to the decay rate eta_c --> gamma gamma and discuss its implications for precision quarkonium physics. We study the suitability of the ratio Gamma(J/psi --> e+e-)/Gamma(eta_c --> gamma gamma), in which the non-perturbative or soft effects cancel at O(alpha_s^{0,1}), 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.

Figures (2)

• Figure 1: Diagrams not considered in this paper: "light-by-light" scattering contributions.
• Figure 2: The second order correction in eq. (\ref{['res1']}) as a function of the charm quark mass.