Radial excitation of light mesons and the γγ* → π0 transition form factor

Abstract

We investigate radial excitation of the quark-antiquark pair in the π0 meson and its effects on the γγ* → π0 transition form factor in the framework of light cone perturbative QCD. The existing constraints on the light cone wave function of the lowest Fock state Iqq¯〉 in the π0 meson allow a sizeable radial excitation of the quark-antiquark pair. We construct the light cone wave function for the quark-antiquark pair in the first radially excited state (the 2S state) using a simple harmonic oscillator potential. The distribution amplitude obtained for the 2S state has two nodes in x at low scale of Q and thereby has a much strong scale dependence than the 1S state. Contributions from this radial excitation to the γγ* → π0 transition form factor exhibit different Q2-dependence behavior from the ground state and thus can modify the prediction for the transition form factor in the medium-large region of Q2.