Forward Cone in Exclusive Heavy Vector Meson Production

Abstract

The color dipole gBFKL phenomenology of a diffraction cone for photo- and electroproduction \(\gamma^{*}N \to VN\) of heavy vector mesons (charmonium & bottonium) at HERA and in fixed target experiments is presented. A substantial shrinkage of the diffraction cone from the CERN/FNAL to the HERA range of c.m.s. energy \(W\) is predicted. 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). An approximate flavor independence of the diffraction slope in the scaling variable \(Q^{2}+m_{V}^{2}\) is shown to hold.