Exclusive production of vector mesons $\rho ,{\rho }^{\prime }$ and ${\rho }^{\prime \prime }$ by real and virtual photons

Abstract

We present a non-perturbative QCD calculation of high-energy diffractive photo- and leptoproduction of vector mesons $\rho$, ${\rho }^{\prime }$ and ${\rho }^{\prime \prime }$ on a nucleon. The initial photon splits up in a $q\bar{q}$-dipole and transforms into a vector meson by scattering on the quark-diquark nucleon. The dipole-dipole scattering amplitude is provided by the non-perturbative model of the stochastic QCD vacuum, the wave functions result from considerations on the light-cone. We assume the physical ${\rho }^{\prime }$- and ${\rho }^{\prime \prime }$-states to be mixed states of an active 2S-excitation and a rest whose coupling to the photon is suppressed. We obtain good agreement with the experimental data and get an understanding of the markedly different spectrum in the ${\pi }^{+}{\pi }^{-}$-invariant mass for photoproduction and $e^{+}{e}^{-}$-annihilation.

Comments: Talk given in Montpellier, QCD Euroconference 98, to be published in the proceedings Nucl.Phys. B (Proc.Suppl.). 5 pages, LaTeX2e, 13 ps/eps figures included, needs style file espcrc2MOD.sty (appended)