A comprehensive analysis of the pion-photon transition form factor in the leading order approximation

We perform a comprehensive analysis of the pion-photon transition form factor F-pi gamma(Q(2)) involving the transverse momentum corrections in the leading order approximation with the present CLEO experimental data, in which the contributions beyond the leading Fock state have been taken into consideration. As is well known, the leading Fock-state contribution dominates of F-pi gamma(Q(2)) at large momentum transfer (Q(2)) region. One should include the contributions beyond the leading Fock state in small Q(2) region. In this paper, we construct a phenomenological expression to estimate the contributions beyond the leading Fock state based on its asymptotic behavior at Q2 -> 0. Our present theoretical results agree well with the experimental data in the whole Q2 region. Then, we extract some useful information of the pionic leading twist-2 distribution amplitude (DA) by comparing our results of Fp(pi gamma)(Q(2)) with the CLEO data. By taking best fit, we have the distribution amplitude moments, a(2)(mu(2)(0)) = 0.002(-0.054)(+0.063), a(4)(mu(2)(0)) = -0.022(-0.012)(+0.026) and all of higher moments, which are closed to the asymptotic-like behavior of the pion wave function.