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.

Comments: 15 pages, 6 figures, use epsfig.sty