Soft-photon radiation in high-energy proton-proton collisions within the tensor-Pomeron approach: Bremsstrahlung

We discuss diffractive processes in proton-proton collisions at small momentum transfers without and with photon radiation. We consider the soft exclusive reactions pp -> pp, p (p) over bar -> p (p) over bar, and pp -> pp gamma within the tensor-Pomeron and vector-odderon approach. We compare our results with the data for pp and p (p) over bar total cross sections, for the ratio of real to imaginary parts of the forward scattering amplitude, and for the elastic pp cross sections, especially those from TOTEM. To describe the low-energy data more accurately, the secondary reggeons must be included. We write down the amplitudes for the photon bremsstrahlung in high-energy proton-proton collisions using the tensor-Pomeron model. These results are relevant for the c.m. energies presently available at the Relativistic Heavy Ion Collider and at the LHC. We present predictions for the proposed measurements of soft photons with the planned future upgrade of the ALICE experiment at the LHC. We investigate the limits of applicability of the soft-photon approximation (SPA) based on Low's theorem. The corresponding SPA results are compared to those obtained from our complete model. The regions of phase space are given quantitatively where SPA and our complete tensor-Pomeron results are close to each other. As an example, let k(perpendicular to), y, and omega, be the absolute value of the transverse momentum, the rapidity, and the energy of the photon, respectively, in the overall c.m. system. For the region 1 MeV < k(perpendicular to) < 100 MeV and 3.5 < vertical bar y vertical bar < 5.0, we find that the SPA Ansatz with only the pole terms proportional to omega(-1) agrees at the percent level with our complete model result up to omega congruent to 2 GeV.

Automated summary

We discuss diffractive processes in proton-proton collisions, both with and without photon radiation, and compare our results with experimental data. The inclusion of secondary reggeons is necessary to accurately describe the low-energy data. We also investigate the photon bremsstrahlung in high-energy proton-proton collisions using the tensor-Pomeron model. These findings are significant for the Relativistic Heavy Ion Collider and the LHC.