Light-by-light scattering in UPC at the LHC

TL;DR

This paper investigates light-by-light scattering in ultraperipheral lead-lead collisions at the LHC, calculating cross sections for different mechanisms and suggesting the feasibility of experimental measurement in specific energy ranges.

Contribution

It provides detailed calculations of diphoton production cross sections in ultraperipheral collisions, including novel contributions from VDM-Regge mechanisms, and assesses their experimental observability.

Findings

High cross section (~306 nb) for diphoton production in PbPb collisions.

Feasibility of measuring elastic gamma-gamma scattering at Wγγ ≈ 15-20 GeV.

Comparison of box diagram and VDM-Regge contributions to the process.

Abstract

We discuss diphoton semi(exclusive) production in ultraperipheral $PbPb$ collisions at energy of $\sqrt{s_{NN}}=$ 5.5 TeV (LHC). 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 two different mechanisms: box diagrams with leptons and quarks in the loops and a VDM-Regge contribution with virtual intermediate hadronic excitations of the photons. We got relatively high cross sections in $PbPb$ collisions ($306$ nb). This opens a possibility to study the $\gamma \gamma \to \gamma \gamma$ (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 $W_{\gamma\gamma} \approx 15-20$ GeV.