English

Pion-photon transition---the new QCD frontier

High Energy Physics - Phenomenology 2011-08-29 v3

Abstract

We perform a detailed analysis of all existing data (CELLO, CLEO, BaBar) on the pion-photon transition form factor by means of light-cone sum rules in which we include the NLO QCD radiative corrections and the twist-four contributions. The NNLO radiative correction together with the twist-six contribution are also taken into account in terms of theoretical uncertainties. Keeping only the first two Gegenbauer coefficients a2a_2 and a4a_4, we show that the 1σ1\sigma error ellipse of all data up to 9 GeV2^2 greatly overlaps with the set of pion distribution amplitudes obtained from nonlocal QCD sum rules---within the range of uncertainties due to twist-four. This remains valid also for the projection of the 1σ1\sigma error ellipsoid on the (a2,a4)(a_2,a_4) plane when including a6a_6. We argue that it is not possible to accommodate the high-Q2Q^2 tail of the BaBar data with the same accuracy, despite opposite claims by other authors, and conclude that the BaBar data still pose a challenge to QCD.

Keywords

Cite

@article{arxiv.1105.2753,
  title  = {Pion-photon transition---the new QCD frontier},
  author = {A. P. Bakulev and S. V. Mikhailov and A. V. Pimikov and N. G. Stefanis},
  journal= {arXiv preprint arXiv:1105.2753},
  year   = {2011}
}

Comments

10 pages, 2 Tables, 4 figures. In v2 some explanations and references added. In v3 some clarifications added and references updated; matches version to appear in Phys. Rev. D

R2 v1 2026-06-21T18:07:05.595Z