Perturbative Effects in the Form Factor γγ^*\to πand Extraction of the Pion Wave Function from CLEO Data

Abstract

We study the pion form factor F^{πγγ^*}(Q^2) 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^*}(Q^2), 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 a_2(μ) = 0.12 \pm 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 a_2 and a_4, which is consistent with the asymptotic distribution amplitude, but does not agree with some old models.