Exclusive diffractive photon bremsstrahlung at the LHC

We calculate differential distributions for the pp -> pp gamma reaction at the LHC energy root s = 14 TeV. We consider diffractive classical bremsstrahlung mechanisms including effects of the non-point-like nature of protons. In addition, we take into account (vector meson)-pomeron, photon-pion, and photon-pomeron exchange processes for the first time in the literature. Predictions for the total cross section and several observables related to these processes, e.g., differential distributions in pseudorapidities and transverse momenta of photons or protons are shown and discussed. The integrated diffractive bremsstrahlung cross section (E-gamma > 100 GeV) is only of the order of mu b. We try to identify regions of the phase space where one of the mechanisms dominates. The classical bremsstrahlung dominates at large forward/backward photon pseudorapidities, close to the pseudorapidities of scattered protons. In contrast, the photon-pomeron (pomeron-photon) mechanism dominates at midrapidities but the related cross section is rather small. In comparison the virtual-omega-rescattering mechanism contributes at smaller angles of photons (larger photon rapidities). Photons in the forward/backward region can be measured by the Zero Degree Calorimeters installed in experiments at the LHC while the midrapidity photons are difficult to measure (small cross section, small photon transverse momenta). Protons could be measured by the ALFA detector (ATLAS) or TOTEM detector at CMS. The exclusivity could be checked with the help of main central detectors.