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 Q ²-controlled sensitivity 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 (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. Zh. éksp. Teor. Fiz. 113, 1930–1962 (June 1998) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.