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 $Q^2<50{\mathrm{GeV}}^2$. 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 $1.3008(\genfrac{}{}{0ex}{}{+73}{-84})$, of the soft Pomeron as $1.0935(\genfrac{}{}{0ex}{}{+76}{-64})$, 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.

• Received 27 March 2019

DOI:https://doi.org/10.1103/PhysRevD.100.114007

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Published by the American Physical Society