Pion-Photon Transition Form Factor and Pion Distribution Amplitude in   QCD: Facing the Enigmatic Behavior of the BaBar Data
  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. 
N. G. Stefanis, Alexander P. Bakulev, S. V. Mikhailov, and A. V.   Pimikov
hep-ph hep-ex hep-lat