Observing light-by-light scattering at the Large Hadron Collider

TL;DR

This paper discusses the potential to observe light-by-light scattering at the LHC, highlighting the expected cross sections, event rates, and the feasibility of measurement in different collision systems.

Contribution

It demonstrates the feasibility of studying elastic light-by-light scattering at the LHC using electromagnetic interactions of protons and lead ions, providing estimated cross sections and event rates.

Findings

Cross sections for $ ext{m}_{ ext{γγ}}>5$ GeV are 105 fb, 260 pb, and 370 nb in p-p, p-Pb, and Pb-Pb collisions.

Approximately 70 signal events per run are expected in Pb-Pb collisions after detector efficiencies.

Light-by-light scattering can be observed with minimal background in Pb-Pb collisions.

Abstract

Elastic light-by-light scattering, $\gamma\gamma\to\gamma\gamma$, is open to study at the Large Hadron Collider thanks to the large quasi-real photon fluxes available in electromagnetic interactions of protons (p) and lead (Pb) ions. The $\gamma\gamma\to\gamma\gamma$ cross sections for diphoton masses $m_{\gamma\gamma} > 5$ GeV amount to 105 fb, 260 pb, and 370 nb in p-p, p-Pb, and Pb-Pb collisions at nucleon-nucleon center-of-mass energies $\sqrt{s_{NN}}$ = 14 TeV, 8.8 TeV, and 5.5 TeV respectively. Such a measurement has no substantial backgrounds in Pb-Pb collisions where one expects about 70 signal events per run, after typical detector acceptance and reconstruction efficiency selections.