Central exclusive diffractive production of a single photon in high-energy proton-proton collisions within the tensor-Pomeron approach

Abstract

We discuss central-exclusive production (CEP) of photons via different fusion processes in the reaction $pp\to pp\gamma$ at high energies, available at RHIC and LHC, within the tensor-pomeron model. We consider two types of processes, the photoproduction contribution via the photon-pomeron and photon-reggeon fusion reactions, and the purely diffractive contribution via the reggeon-pomeron and odderon-pomeron fusion reactions. We present predictions for the measurements of photons at midrapidity, $|\mathrm{y}|<2.5$, and at relatively low transverse momentum, $0.1\mathrm{GeV}<k_{\perp }<1\mathrm{GeV}$. To check the main results of our study the measurement of the outgoing protons is not necessary. This is of relevance, e.g., for the present version of the ALICE detector at the LHC. Several differential distributions, for instance, in $\mathrm{y}$, $k_{\perp }$ and $\omega$, the rapidity, the absolute value of the transverse momentum, and the energy of the photon, respectively, are presented. We show that the photoproduction is an important process in the kinematic region specified above. There it gives a much larger cross section than diffractive bremsstrahlung. This is remarkable as the CEP cross section is of order ${\alpha }_{\mathrm{em}}^3$ whereas the bremsstrahlung one is only of order ${\alpha }_{\mathrm{em}}$. On the other hand, the soft-photon bremsstrahlung where the basic $pp\to pp$ reaction is due to strong interaction diffraction is more important than CEP in the forward rapidity range, $|\mathrm{y}|>4$, and/or at very low $k_{\perp }$. We leave it as a challenge for the planned ALICE 3 experiment at the LHC to study these two contributions to soft photon production in $pp$ collisions. This could shed new light on the so called ``soft photon puzzle'' in hadron-hadron collisions.

27 pages, 13 figures

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Cited by in corpus (6)

• Dark photon production via elastic proton bremsstrahlung with non-zero momentum transfer
• Different versions of soft-photon theorems exemplified at leading and next-to-leading terms for pion-pion and pion-proton scattering
• Exclusive diffractive bremsstrahlung of one and two photons at forward rapidities: Possibilities for experimental studies in $pp$ collisions at the LHC
• Soft-photon theorem for pion-proton elastic scattering revisited
• Anomalous and Linear Holographic Hard Wall Models for Glueballs and the Pomeron
• Exclusive process $\gamma \gamma \to J/\psi +\gamma$ production in ultraperipheral proton and nuclear collisions at the HL-LHC and FCC