Constraints on the light pseudoscalar meson distribution amplitudes from their meson-photon transition form factors

The meson-photon transition form factors gamma gamma* -> P (P stands for pi, eta and eta') provide strong constraints on the distribution amplitudes of the pseudoscalar mesons. In this paper, these transition form factors are calculated under the light-cone perturbative QCD approach, in which both the valence and nonvalence quarks' contributions have been taken into consideration. To be consistent, a unified wave function model is adopted to analyze these form factors. It is shown that with the proper charm component f(eta')(c) similar to -30 MeV and a moderate DA with B similar to 0.30, the experimental data on Q(2)F (eta gamma)(Q(2)) and Q(2)F (eta'gamma)(Q(2) ) in the whole Q(2) region can be explained simultaneously. Furthermore, a detailed discussion on the form factors' uncertainties caused by the constituent quark masses m(q) and m(s), the parameter B, the mixing angle phi, and f(eta')(c) are presented. It is found that, by adjusting these parameters within their reasonable regions, one can improve the form factor to a certain degree but cannot solve the puzzle for Q(2)F (pi gamma)(Q(2)), especially to explain the behavior of the pi - gamma form factor within the whole Q(2) region consistently. We hope further experimental data on these form factors in the large Q(2) region can clarify the present situation.