Properties of the quark-antiquark-gluon Fock state in the \eta_c meson
  In this paper the twist-3 distribution amplitude of the quark-antiquark-gluon Fock state in the \eta_c meson is studied. To calculate the moments of this distribution amplitude QCD sum rules is applied. Using the results of the calculation the model of this distribution amplitude is built. In addition NRQCD matrix elements which determine the properties of the quark-antiquark-gluon Fock state are determined. In particular, the probability amplitude to find the quark-antiquark pair in the color octet state, the mean gluon energy and the fraction of momentum carried by gluon, the relative velocity of the color-octet quark-antiquark-pair are calculated. 
V. V. Braguta
hep-ph