Abstract
The pion electromagnetic form factor is calculated in the space- and time-like regions from −10 (GeV/c)2 up to 10 (GeV/c)2, within a front-form model. The dressed photon vertex where a photon decays in a quark–antiquark pair is depicted generalizing the vector meson dominance ansatz, by means of the vector meson vertex functions. An important feature of our model is the description of the on-mass-shell vertex functions in the valence sector, for the pion and the vector mesons, through the front-form wave functions obtained within a realistic quark model. The theoretical results show an excellent agreement with the data in the space-like region, while in the time-like region the description is quite encouraging.
Highlights
In the framework of the front-form dynamics [1] a large number of papers has been devoted to the study of the electromagnetic form factor of the pion, mostly dealing with the space-like (SL) region [4,5,6,7,8,9,10]
In this Letter, the pion electromagnetic form factor is evaluated within the front-form dynamics, in both the SL and the TL regions, by using as a starting point the Mandelstam formula [12] for the triangle diagrams of Figs. 1 and 2
Our aim is to investigate the possibility of describing the photon–hadron interaction by applying the vector meson (VM) dominance ansatz at the level of the photon vertex function
Summary
In the framework of the front-form dynamics [1] (see, e.g., [2,3] for extensive reviews) a large number of papers has been devoted to the study of the electromagnetic form factor of the pion, mostly dealing with the space-like (SL) region [4,5,6,7,8,9,10]. Mn2 + ıMnΓn(q where fV n is the decay constant of the nth vector meson in a virtual photon (see below), Mn the corresponding mass, Pn the VM total momentum (Pnμ ≡ {Pn− = (|q⊥|2 + Mn2)/q+, Pn⊥ = q⊥, Pn+ = q+}; note that at the production vertex, see Fig. 3, the front-form three-momentum is conserved), and λ the VM polarization.
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