English

Chiral anomaly, triangle loop and the the $\gamma\gamma^{*}\to \pi^{0}$ form factor

High Energy Physics - Phenomenology 2011-03-07 v2 High Energy Physics - Experiment

Abstract

The recent BaBar measurements of the γγπ0\gamma\gamma^{*}\to \pi^{0} form factor show spectacular deviation from perturbative QCD computations for large space-like Q2Q^{2}. At 34GeV234\,\rm GeV^{2} the data are more than 50% larger than theoretical predictions. Stimulated by these new experimental results, we revisit our previous paper on triangle loop effects related to chiral anomaly, and apply our method to the γ+γπ0\gamma + \gamma^* \to \pi^0 form factor measured in the single tag mode e++ee++e+π0e^{+} + e^{-}\to e^{+} + e^{-} + \pi^{0} with one highly virtual photon. The resultant form factor F(Q2)F(Q^{2}) - which depends on only one parameter (the mass mm of up, down quark circulating in the triangle loop) behaves like (m2Q2)×(ln(Q2/m2))2(\frac{m^{2}}{Q^{2}})\times (\ln(Q^{2}/m^{2}))^{2} - shows a striking agreement with BaBar data for m132MeVm \approx 132\,\rm MeV. The rising logarithm squared form factor, surprisingly unnoticed in the literature, is in sharp contrast with the rather flat ones derived from perturbative QCD approaches.

Keywords

Cite

@article{arxiv.1103.0452,
  title  = {Chiral anomaly, triangle loop and the the $\gamma\gamma^{*}\to \pi^{0}$ form factor},
  author = {T. N. Pham and X. Y. Pham},
  journal= {arXiv preprint arXiv:1103.0452},
  year   = {2011}
}

Comments

v2,9 pages, 1 figure included in pdf file, references added