Exploratory study of shrinkage of the diffraction cone for the generalized BFKL pomeron

In color dipole gBFKL dynamics, we describe the emerging gBFKL phenomenology of a subasymptotic energy dependence of the diffraction slope and discuss possibilities of testing the gBFKL predictions in exclusive photo- and electroproduction of vector mesons $V$ at HERA. A substantial shrinkage of the diffraction cone $\gamma^{*}p\rightarrow Vp$ processes from the CERN/FNAL to HERA range of energy $W$ is predicted. This subasymptotic shrinkage is faster than expected from the small slope of pomeron's Regge trajectory $\alpha_{\Pom}'$. We point out that the diffraction slope is a scaling function of $(m_{V}^{2}+Q^{2})$, what relates production of different vector mesons.