Pion transition form factor at the two-loop level vis-\`a-vis experimental data

TL;DR

This paper calculates the pion-photon transition form factor using advanced QCD sum rules with radiative corrections, compares predictions with experimental data, and discusses potential violations of QCD factorization.

Contribution

It provides a next-to-next-to-leading order calculation of the form factor and critically compares it with experimental data, highlighting discrepancies with the BaBar results.

Findings

BaBar data are incompatible with QCD convolution scheme

Predictions agree with CELLO and CLEO data

Possible violation of factorization theorem suggested

Abstract

We use light-cone QCD sum rules to calculate the pion-photon transition form factor, taking into account radiative corrections up to the next-to-next-to-leading order of perturbation theory. We compare the obtained predictions with all available experimental data from the CELLO, CLEO, and the BaBar Collaborations. We point out that the BaBar data are incompatible with the convolution scheme of QCD, on which our predictions are based, and can possibly be explained only with a violation of the factorization theorem. We pull together recent theoretical results and comment on their significance.