Role of the non-resonant background in the $\rho^0$-meson diffractive electro- and photoproproduction

Abstract

The background due to the direct diffractive dissociation of the photon into the $\pi^+\pi^-$-pair to the "elastic" diffractive $\rho^0$-meson production in electron-proton collisions is calculated. The amplitude for the background process $\gamma p \to \pi^+ \pi^- p$ is proportional to the $\pi$-meson - proton cross section. Therefore, describing the HERA data, we can estimate $\sigma (\pi p)$ at energy $s_{\pi p}\sim (2 - 3) \times 10^{3}$ GeV$^2$ that is considerably higher the existing data. At large $Q^2$ the interference between resonant and non-resonant $\pi^+ \pi^-$ production leads also to the more slow increase of the $\sigma^L/\sigma^T$ ratio with the mass of the $2\pi$ (i.e. $\rho^0$-meson) state.