The diffraction cone for exclusive vector meson production in deep inelastic scattering

Abstract

We develop the color dipole gBFKL phenomenology of a diffraction cone for photo- and electroproduction ${\gamma }^{\ast }N\to VN$ of heavy vector mesons (charmonium & bottonium) at HERA and in fixed target experiments. We predict a substantial shrinkage of the diffraction cone from the CERN/FNAL to the HERA range of c.m.s. energy $W$. The $Q^2$-controlled selectivity to the color dipole size (scanning phenomenon) is shown to lead to a decrease of the diffraction slope with $Q^2$ (which is supported by the available experimental data). We predict an approximate flavor independence of the diffraction slope in the scaling variable $Q^2+m_V^2$. For diffractive production of the radially excited $2S$ states (${\Psi }^{\prime },{{\rm Y}}^{\prime }$) the counterintuitive inequality of diffraction slopes $B(2S)\text{lsim}B(1S)$ is predicted, which defies the common wisdom that diffraction slopes are larger for reactions with larger size particles.

Comments: 36 pages, 19 figures