The photon-pion transition form factor: incompatible data or incompatible models?

Abstract

The elastic and $\gamma \to \pi$ transition form factors of the pion along with its usual static observables are calculated within a light-front field approach to the constituent quark model. The focus of this exercise in a simple model is on a unified description of all observables with one singly parametrized light-front wave function to detect possible discrepancies in experimental data, in particular the contentious large momentum-squared data on the transition factor as reported by BaBar and Belle. We also discuss the relation of a small to vanishing pion charge radius with an almost constant pion distribution amplitude and compare our results with those obtained in a holographic light-front model.

Comments: Invited contribution to the Light Cone 2013 Conference in Skiathos, Greece, 20-24 May 2013. 7 pages, two figures