Tensor Pomeron and low-x deep inelastic scattering

The tensor-Pomeron model is applied to low-x deep inelastic lepton-nucleon scattering and photoproduction. We consider c.m. energies in the range 6-318 GeV and Q(2) < 50 GeV2. In addition to the soft tensor Pomeron, which has proven quite successful for the description of soft hadronic high-energy reactions, we include a hard tensor Pomeron. We also include f(2)-Reggeon and a(2)-Reggeon exchange. The sum of these latter exchanges turns out to be particularly relevant for real-photon-proton scattering at c.m. energies in the range up to 30 GeV. The combination of all these exchanges permits a description of the absorption cross sections of real and virtual photons on the proton in the same framework. In particular, a detailed comparison of this two-tensor-Pomeron model with the latest HERA data for x < 0.01 is made. Our model gives a very good description of the transition from the small-Q(2) regime where the real or virtual photon behaves hadronlike to the large-Q(2) regime where hard scattering dominates. Our fit allows us, for instance, a determination of the intercepts of the hard Pomeron as 1.3008((+73)(-84)), of the soft Pomeron as 1.0935((+76)(-64)) and of the f(2) plus a(2) Reggeons. We find that in photoproduction the hard Pomeron does not contribute within the errors of the fit. We show that assuming a vector instead of a tensor character for the Pomeron leads to the conclusion that it must decouple in real photoproduction and in the DIS structure functions.