Exclusive Bremsstrahlung of One and Two Photons in Proton-Proton Collisions

Abstract

We discuss the diffractive bremsstrahlung of a single photon in the $pp\to pp\gamma$ reaction at LHC energies and at forward photon rapidities. We compare the results for our standard approach, based on QFT and the tensor-Pomeron model, with two versions of soft-photon approximations, SPA1 and SPA2, where the radiative amplitudes contain only the leading terms proportional to ${\omega }^{-1}$ (the inverse of the photon energy). SPA1, which does not have the correct energy-momentum relations, performs surprisingly well in the kinematic range considered, namely at very forward photon rapidities and $0.02<{\xi }_{1,2}<0.1$, the relative energy loss of the protons, corresponding to small values of the photon transverse momentum. Azimuthal correlations between outgoing particles are presented. We discuss also the role of the $pp\to pp{\pi }^0$ background for single photon production. We discuss also the possibility of a measurement of the $pp\to pp\gamma \gamma$ reaction. Our predictions can be verified by ATLAS-LHCf combined experiments.

Comments: 10 pages, 6 figures, presented by A. Szczurek at XXX Cracow EPIPHANY Conference on Precision Physics at High Energy Colliders, Krakow, Poland, January 8-12, 2024