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 γ∗p → 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 pomeronʹs Regge trajectory α′p. We point out that the diffraction slope is a scaling function of (mv2 + Q2), which relates production of different vector mesons.