Color dipole phenomenology of diffractive electroproduction of light vector mesons at HERA

Abstract

We develop the color dipole phenomenology of diffractive photo- and electroproduction $γ^{*}\,N\rightarrow V(V')\,N$ of light vector mesons ($V(1S)=\ddot{I}{•}^0,\ddot{I}{‰}^0,\ddot{I}{}^0$) and their radial excitations ($V^{\prime }(2S)=\ddot{I}{•}^{\prime },\ddot{I}{‰}^{\prime },\ddot{I}{}^{\prime }$). The node of the radial wave function of the $2S$ states in conjunction with the energy dependence of the color dipole cross section is shown to lead to a strikingly different $Q^2$ and $\hat{I}½$ dependence of diffractive production of the $V(1S)$ and $V^{\prime }(2S)$ vector mesons. We discuss the restoration of flavor symmetry and universality properties of production of different vector mesons as a function of $Q^2+m_V^2$. The color dipole model predictions for the $\ddot{I}{}^0$ and $\ddot{I}{•}^0$ production are in good agreement with the experimental data from the EMC, NMC, ZEUS and H1 collaborations. We present the first direct evaluation of the dipole cross section from these data.

39 pages LaTeX, 18 figures in bitmapped postscript, uuencoded. The original postscript figures are available at ftp://ftp.to.infn.it/pub/giunti/jan/