$\gamma\gamma \to \gamma \gamma$ scattering in ultrarelativistic UPC

TL;DR

This paper analyzes light-by-light scattering in ultraperipheral collisions at the LHC and FCC, calculating cross sections for various mechanisms and comparing predictions with experimental data.

Contribution

It provides detailed predictions for diphoton production cross sections and distributions in ultrarelativistic collisions, including multiple mechanisms, and compares them with recent experimental results.

Findings

High cross sections for heavy ion collisions enable light-by-light scattering studies.

Elastic $ ext{γγ}$ scattering measurable up to 15-20 GeV invariant mass.

Standard Model predictions align with recent ATLAS measurements.

Abstract

We discuss diphoton semi(exclusive) production in ultraperipheral lead-lead collisions at energy of $\sqrt{s_{NN}}$ = 5.5 TeV (LHC) and in proton-proton collisions at $\sqrt{s_{pp}}$ = 7 TeV (LHC) and $\sqrt{s_{pp}}$ = 100 TeV (FCC). The nuclear calculations are based on equivalent photon approximation in the impact parameter space. The cross sections for elementary $\gamma\gamma \to \gamma\gamma$ subprocess are calculated including three different mechanisms: box diagrams with leptons and quarks in the loops, a VDM-Regge contribution with virtual intermediate hadronic excitations of the photons and the two-gluon exchange contribution. We get relatively high cross sections in heavy ion collisions. This opens a possibility to study the light-by-light (quasi)elastic scattering at the LHC. We find that the cross section for elastic $\gamma\gamma$ scattering could be measured in the lead-lead collisions for the diphoton invariant mass up to $W_{\gamma\gamma} \approx$ 15 - 20 GeV. Our Standard Model predictions are compared to a recent ATLAS experimental result. We present differential distributions for PbPb$\to$PbPb$\gamma\gamma$ and pp$\to$pp$\gamma\gamma$ reaction.