Flavor Symmtry Breaking andd Mixing Effects in the eta-gamma and eta'-gamma Transition Form Factors

Abstract

We reanalyze the eta-gamma and eta&#39;-gamma transition form factors within the modified hard scattering approach on the basis of new experimental data from CLEO and L3. Our approach perfectly describes the experimental data over a wide range of the virtuality of the probing photon, 1 GeV^2 < Q^2 < 15 GeV^2. The analysis provides hints that the conventional flavor octet-singlet scheme for the eta-eta&#39; mixing is too simple. A more general mixing scheme on the other hand, involving two mixing angles, leads to a very good description of the transition form factors and also accounts for the two-photon decay widths of the eta and eta&#39; mesons as well as for the ratio of the widths for the J/Psi --> eta&#39; gamma and J/Psi --> eta gamma decays. We also investigate the questions of possible deviations of the eta and eta&#39; distribution amplitudes from the asymptotic form and of eventual intrinsic charm in the eta and eta&#39; mesons. We estimate the charm decay constant of the eta&#39; meson to lie within the range -65 MeV < fc(eta&#39;) <15 MeV.