Accessing the pion distribution amplitude through the CLEO and E791 data

Abstract

Using QCD perturbation theory in NLO and light-cone QCD sum rules, we extract from the CLEO experimental data on the F^{γ^*γπ}(Q^{2} transition form factor constraints on the Gegenbauer coefficients a_2 and a_4, as well as on the inverse moment <x^{-1}>_π of the pion distribution amplitude. We show that both the asymptotic and the Chernyak--Zhitnitsky pion distribution amplitudes are excluded at the 3σ- and 4σ-level, respectively, while the data confirms the end-point suppressed shape of the pion DA we previously obtained with QCD sum rules and nonlocal condensates. These findings are also supported by the data of the Fermilab E791 experiment on diffractive dijet production.