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

We develop the color dipole gBFKL phenomenology of a diffraction cone for photo-and electroproduction γ*N−VN of heavy vector mesons (charmonium & bottomonium) 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 Q2-controlled sensitivity to the color dipole size (scanning phenomenon) is shown to lead to a decrease of the diffraction slope with Q2 (which is supported by the available experimental data). We predict an approximate flavor independence of the diffraction slope in the scaling variable Q2+mV2. For diffractive production of the radially excited 2S states (Ψ′, γ′), a counterintuitive inequality of diffraction slopes B(2S)≲B(1S) is predicted, which defies the common wisdom that diffraction slopes are larger for reactions with larger size particles.