The η (η′) gamma transition form factor and the gluon–gluon distribution amplitude

Abstract

The ηγ and η′γ transition form factors are analyzed to leading-twist accuracy and next-to-leading order of perturbative QCD. Using an η–η′ mixing scheme and all currently available experimental data the lowest Gegenbauer coefficients of the distribution amplitudes for the valence octet and singlet and the gluon–gluon Fock components are extracted. Predictions for the g*g*η′ vertex function are presented. We also comment on the new BELLE results for the πγ transition form factor.