\eta-\eta' -Glueball mixing from photon-meson transition form factors and decay ratio D_s --> \eta l \nu / \eta' l \nu

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 $s_{\pi p}\sim (2-3)10^{3}Ge{V}^2$ 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: Twocoloumn Revtex, 5 pages, 5 figures, 12 .eps files