Perturbative Effects in the Form Factor \gamma\gamma^*\to \pi and Extraction of the Pion Wave Function from CLEO Data

TL;DR

This paper analyzes the pion form factor using light-cone sum rules, incorporating radiative and higher twist effects, to extract the pion distribution amplitude from CLEO data, finding it close to the asymptotic form.

Contribution

It provides a novel extraction of the twist-2 pion distribution amplitude from experimental data, including radiative corrections and higher twist effects.

Findings

The deviation of the pion distribution amplitude from the asymptotic form is small.

The estimated parameter a_2(0)=0.12 b1 0.03 at
60=2.4 GeV.

The two-term non-asymptotic ansatz is consistent with the asymptotic form but not with some older models.

Abstract

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 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(\mu) = 0.12 \pm 0.03 at \mu=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.