Pion-Photon Transition Form Factor and Pion Distribution Amplitude in QCD: Facing the Enigmatic Behavior of the BaBar Data

TL;DR

This paper analyzes experimental data on the pion-photon transition form factor, highlighting discrepancies with standard QCD predictions, especially regarding BaBar data, and discusses the challenges in reconciling these findings within current theoretical frameworks.

Contribution

The paper provides an extended analysis of experimental data and discusses the difficulty of explaining BaBar's anomalous results within standard QCD.

Findings

BaBar data shows divergent behavior not explained by standard QCD

Standard QCD framework cannot self-consistently accommodate the BaBar data

Discussion of various theoretical approaches and their limitations

Abstract

We present an extended analysis of the data for the pion-photon transition form factor from different experiments, CELLO, CLEO, and BaBar, and discuss various theoretical approaches which try to reason from them. We focus on the divergent behavior of the BaBar data for the pion and those for the $\eta(\eta')$ pseudoscalar mesons and comment on recently proposed explanations for this discrepancy. We argue that it is not possible at present to accommodate these data within the standard QCD framework self-consistently.