Perturbative Effects in the Form Factor γγ∗ → π and Extraction of the Pion Distribution Amplitude from CLEO Data

We study the pion form factor F πγγ ∗ (Q2) in the light-cone sum rule approach, accounting for radiative corrections and higher twist effects. Comparing the results to the CLEO experimental data on F πγγ ∗ (Q2), we extract the the pion distribution amplitude of twist-2. The deviation of the distribution amplitude from the asymptotic one is small and is estimated to be a2(μ) = 0.12± 0.03 at μ = 2.4 GeV, in the model with one non-asymptotic term. The ansatz with two non-asymptotic terms gives some region of a2 and a4, which is consistent with the asymptotic distribution amplitude, but does not agree with some old models. PACS numbers: 11.55.Hx, 12.38.Bx, 13.40.Gp, 14.40.Aq e-mail: [email protected] e-mail: [email protected]