Perturbative effects in the form factorγγ*→π0and extraction of the pion distribution amplitude from CLEO data

We study the pion form factor $F^{\pi \gamma {\gamma }^{*}}{(Q}^2)$ in the light-cone sum rule approach, accounting for radiative corrections and higher twist effects. Comparing the results to the CLEO experimental data on $F^{\pi \gamma {\gamma }^{*}}{(Q}^2),$ we extract the pion distribution amplitude of twist 2. The deviation of the distribution amplitude from the asymptotic one is small and is estimated to be $a_2\left(\mu \right)=0.12\mathrm{}\pm 0.03$ at $\mu =2.4\mathrm{}$ GeV, in the model with one nonasymptotic term. The ansatz with two nonasymptotic 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.