Phenomenology developments in UPC: $\gamma \gamma \to \gamma \gamma$ scattering

TL;DR

This paper explores extensions of gamma-gamma scattering studies in ultraperipheral heavy ion collisions, including inelastic processes and single photon production, with implications for future detector experiments.

Contribution

It proposes studying inelastic gamma-gamma processes and associated neutron production, expanding current coherent process analyses in ultraperipheral collisions.

Findings

Inelastic processes constitute 20-30% of total gamma-gamma scattering.

Cross sections for single photon production are calculated for various mechanisms.

Deviations from predictions could indicate inelastic contributions.

Abstract

We discuss several possible extensions of present studies of $\gamma \gamma \to \gamma \gamma$ scattering in ultraperipheral heavy ion collisions. One of the possible extensions are studies for lower diphoton invariant masses (smaller transverse momenta). There new mechanisms may show up. This includes possible studies with future FOCAL and ALICE 3 detectors. So far only coherent $\gamma \gamma \to \gamma \gamma$ processes, when initial photons couple to nuclei, were sudied theoretically. Recently we proposed to study also inelastic processes, when initial photons couple to individual nucleons. Without special cuts the corresponding processes are of the order of 20 - 30 \%. A study to which extent the inelastic processes survive with the present cuts used for the $\gamma \gamma \to \gamma \gamma$ studies is an interesting question. They can be of interest by itself and dedicated studies are suggested. We calculate also cross section for associated neutron production. Deviation from our predictions could signal presence of the inelastic contribution. Finally we discuss production of single photons in UPC ($A A \to A A \gamma$). Corresponding cross sections for selected mechanisms are presented.