Chiral Anomaly, Triangle Loop and the \(\gamma\gamma^{*}\to \pi^{0}\) Transition Form Factor

Pham Tri Nang, Pham Xuan Yem
Author affiliations

Authors

  • Pham Tri Nang Centre de Physique Théorique, CNRS, Ecole Polytechnique, 91128 Palaiseau, France
  • Pham Xuan Yem Laboratoire de Physique Théorique et Hautes Energies, Université Pierre &Marie Curie, Unité associée au CNRS, 75005 Paris, France

DOI:

https://doi.org/10.15625/0868-3166/22/4/2554

Abstract


The recent BaBar measurements of the \(\gamma +\gamma ^{ * }  \to \pi ^{0 }\) form factor show spectacular deviation from perturbative QCD computations for large space-like \(Q^{2}\). At 34 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 \(\gamma +\gamma ^{ * }  \to  \pi ^{0 }\) transition form factor measured in the single tag mode \(e^{ + }+e^{ - } \to   e^{ + }+ e^{ - }+\pi ^{0 }\) with one highly virtual photon \(\gamma ^{ * }\). The resultant form factor \(F(Q^{2})\)- which depends on only one parameter (the mass \(m\) of up, down quark circulating in the triangle loop) behaves like \((m^{2}/Q^{2}) \times  [\ln (Q^{2}/m^{2})]^{2}\)- shows a striking agreement with BaBar data for \(m \approx   132\) 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.

Downloads

Download data is not yet available.

Metrics

Metrics Loading ...

Downloads

Published

10-01-2013

How to Cite

[1]
P. T. Nang and P. X. Yem, “Chiral Anomaly, Triangle Loop and the \(\gamma\gamma^{*}\to \pi^{0}\) Transition Form Factor”, Comm. Phys., vol. 22, no. 4, p. 289, Jan. 2013.

Issue

Section

Papers
Received 12-11-2012
Accepted 21-11-2012
Published 10-01-2013