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

摘要

The elastic and $\gamma \to \pi$ transition form factors of the pion alongwith its usual static observables are calculated within a light-front fieldapproach to the constituent quark model. The focus of this exercise in a simplemodel is on a unified description of all observables with one singlyparametrized light-front wave function to detect possible discrepancies inexperimental data, in particular the contentious large momentum-squared data onthe transition factor as reported by BaBar and Belle. We also discuss therelation of a small to vanishing pion charge radius with an almost constantpion distribution amplitude and compare our results with those obtained in aholographic light-front model.