Vector mesons $\rho, \rho'$ and $\rho''$ diffractively photo- and leptoproduced

Abstract

In the framework of non-perturbative QCD we calculate high-energy diffractive production of vector mesons $\rh, \rh'$ and $\rh''$ by real and virtual photons on a nucleon. The initial photon dissociates into a $q\bar{q}$-dipole and transforms into a vector meson by scattering off the nucleon which, for simplicity, is represented as quark-diquark. The relevant dipole-dipole scattering amplitude is provided by the non-perturbative model of the stochastic QCD vacuum. The wave functions result from considerations in the frame of light-front dynamics; the physical $\rh'$- and $\rh''$-mesons are assumed to be mixed states of an active 2S-excitation and some residual rest (2D- and/or hybrid state). We obtain good agreement with the experimental data and get an understanding of the markedly different $\pi^+\pi^-$-mass spectra for photoproduction and $e^+e^-$-annihilation.