Direct calculation of the triple-pomeron coupling for diffractive deep inelastic scattering and real photoproduction

The authors present a unified direct evaluation of the triple-pomeron coupling A3P(Q2) for diffractive real photoproduction (Q2 = 0) and deep inelastic scattering at large Q2 in the framework of the dipole approach to the generalized BFKL pomeron. They demonstrate how the reaction mechanism changes from diffraction excitation of the constituent quarks of the photon at Q2 = 0 to excitation of the octet-octet color dipole state of the virtual photon at large Q2. The small phenomenological value of A3P(0), which was a mystery, is related to the small nonperturabative correlation radius Rc∼0.3 fm for the perturbative gluons. The authors confirm the early expectations of weak Q2 dependence of the dimensional coupling A3P(Q2) and predict that it rises by the factor ∼1.6 from real photoproduction to deep inelastic scattering. 23 refs., 1 fig