Electromagnetic form factor of the pion in the field-theory-inspired approach

Abstract

A new expression for the pion form factor ${F}_{\ensuremath{\pi}}$ is proposed. It takes into account the pseudoscalar meson loops and the mixing of $\ensuremath{\rho}(770)$ with heavier $\ensuremath{\rho}(1450)$ and $\ensuremath{\rho}(1700)$ resonances. The expression has correct analytical properties and can be used in both timelike and spacelike kinematical regions. The comparison is made with the existing experimental data on ${F}_{\ensuremath{\pi}}$, collected with the detectors SND, CMD-2, KLOE, and the BABAR, restricted to energies below 1 GeV. A good description of all four data sets is obtained. In the spacelike region, upon substituting the resonance parameters found in the timelike one, one obtains ${F}_{\ensuremath{\pi}}$, in agreement with the measurements of the NA7 Collaboration.