A combined study of the pion's static properties and form factors

Abstract

We study consistently the pion's static observables and the elastic and γ*γ-> π^0 transition form factors within a light-front model. Consistency requires that all calculations are performed within a given model with the same and single adjusted length or mass-scale parameter of the associated pion bound-state wave function. Our results agree well with all extent data including recent Belle data on the γ*γ-> π^0 form factor at large q^2, yet the BaBar data on this transition form factor resists a sensible comparison. We relax the initial constraint on the bound-state wave function and show the BaBar data can partially be accommodated. This, however, comes at the cost of a hard elastic form factor not in agreement with experiment. Moreover, the pion charge radius is about 40% smaller than its experimentally determined value. It is argued that a decreasing charge radius produces an ever harder form factor with a bound-state amplitude difficultly reconcilable with soft QCD. We also discuss why vector dominance type models for the photon-quark vertex, based on analyticity and crossing symmetry, are unlikely to reproduce the litigious transition form factor data.

arXiv comment14 pages, 7 figures, 2 Tables; minor changes; 2 new references added (Ref. 54 and 57); version to be published in Few Body Physics

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• Exploring the light-quark interaction
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• The pion: an enigma within the Standard Model
• Structure of the neutral pion and its electromagnetic transition form factor
• Pion distribution amplitude from lattice-QCD
• Exciting flavored bound states
• Partonic structure of neutral pseudoscalars via two photon transition form factors
• Charmed mesons with a symmetry-preserving contact interaction
• Distribution Amplitudes of Heavy Mesons and Quarkonia on the Light Front
• On the large-Q^2 behavior of the pion transition form factor
• Mass spectrum and decay constants of radially excited vector mesons
• Pion structure in the nuclear medium
• Excited hadrons and the analytical structure of bound-state interaction kernels
• Spacelike and timelike form factors for the $({\pi }^0,\eta ,{\eta }^{\prime })\to {\gamma }^{\ast }\gamma$ transitions in the light-front quark model
• Couplings between the $\rho$ and $D$- and $D^{\ast }$-mesons
• Pseudoscalar mesons with symmetric bound state vertex functions on the light front
• The pion distribution amplitude and the pion-photon transition form factor in a nonlocal chiral quark model
• Matching lightcone- and anomaly-sum-rule predictions for the pion-photon transition form factor
• The photon-pion transition form factor: incompatible data or incompatible models?
• Deuteron electromagnetic form factors in transverse plane with a phenomenological Lagrangian approach
• Contemporary continuum QCD approaches to excited hadrons
• The Charm and Beauty of Strong Interactions
• Theoretical description and measurement of the pion-photon transition form factor
• Electromagnetic spin-1 form-factor free of zero-modes
• Pion observables calculated in Minkowski and Euclidean spaces with Ansätze for quark propagators
• Parton distribution and fragmentation functions with massive gluons
• Electromagnetic decays of the neutral pion investigated in the Dyson-Schwinger formalism