A new gamma*-p / pbar-p factorization test in diffraction, valid below Q^2 about 6 GeV^2

One of the key experimental issues in Pomeron physics is the extent to which factorization of Pomeron emission and interaction is valid in diffractive processes. In the present paper, we present the results of a new test in diffractive gamma*-p and pbar-p interactions, which does not rely on the assumption of universality of the Pomeron flux factor in the proton. The test is satisfied to within ~20% for 1 < Q^2 ~ 6 GeV^2 and beta < 0.4 in the gamma*-p interactions, suggesting that multi-Pomeron-exchange has a limited effect on factorization. However, a clear breakdown is observed at larger Q^2. Kharzeev and Levin suggest that this can be attributed to the onset of perturbative QCD effects due to the Pomeron's structure. The breakdown occurs in a Q^2 region which agrees with their estimates of a small Pomeron size.