Pion-photon transition form factor using light-cone sum rules: theoretical results, expectations, and a global-data fit

TL;DR

This paper performs a comprehensive global analysis of pion-photon transition form factor data using light-cone sum rules, incorporating higher-order QCD corrections and uncertainties, to investigate the pion distribution amplitude and address discrepancies in high-Q^2 data.

Contribution

It provides a detailed theoretical analysis including higher-order corrections and fits to experimental data, highlighting challenges in explaining high-Q^2 BaBar data within standard models.

Findings

Standard fits cannot fully accommodate BaBar high-Q^2 data

The analysis constrains the pion distribution amplitude characteristics

Theoretical uncertainties are systematically included in the fit

Abstract

A global fit to the data from different collaborations (CELLO, CLEO, BaBar) on the pion-photon transition form factor is carried out using light-cone sum rules. The analysis includes the next-to-leading QCD radiative corrections and the twist-four contributions, while the main next-to-next-to-leading term and the twist-six contribution are taken into account in the form of theoretical uncertainties. We use the information extracted from the data to investigate the pivotal characteristics of the pion distribution amplitude. This is done by dividing the data into two sets: one containing all data up to 9 GeV$^2$, whereas the other incorporates also the high-$Q^2$ tail of the BaBar data. We find that it is not possible to accommodate into the fit these BaBar data points with the same accuracy and conclude that it is difficult to explain these data in the standard scheme of OCD.