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, pp¯→pp¯, and pp→ppγ within the tensor-Pomeron and vector-odderon approach. We compare our results with the data for pp and pp¯ 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⊥, y, and ω, 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 1MeV<k⊥<100MeV and 3.5<|y|<5.0, we find that the SPA Ansatz with only the pole terms ∝ω−1 agrees at the percent level with our complete model result up to ω≅2GeV.

• Received 17 June 2022
• Accepted 12 July 2022

DOI:https://doi.org/10.1103/PhysRevD.106.034023

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society