Information on the pion distribution amplitude from the pion-photon transition form factor with the Belle and BABAR data

Abstract

We perform an analysis of all existing experimental data on the pion-photon transition form factor (TFF). In the calculation, we include the next-to-leading order correction to the valence-quark contribution and estimate the non-valence-quark contribution by a phenomenological model based on the TFF's limiting behavior at both Q2 → 0 and Q2 → ∞. At present, the pion distribution amplitude (DA) is not definitely determined, it is helpful to have a pion DA model that can mimic all the behaviors suggested in the literature. For the purpose, we adopt the conventional model for pion wavefunction/DA whose broadness is dominantly controlled by a single parameter B. We fix the DA parameters by using the CELLO, CLEO, BABAR and Belle data within small Q2 region (Q2 ≤ 15 GeV2), where all the data are consistent with each other. The pion-photon TFF is then extrapolated into a larger Q2 region. It is found that we still need more data at a large Q2 region in order to determine the precise value of B, and we hope that the definite behavior of pion DA can be concluded finally by the consistent data in the coming future.