# Photon-photon scattering in the resonance region at midrapidity at the LHC

## TL;DR

This paper investigates photon-photon scattering in ultra-peripheral lead-lead collisions at the LHC, focusing on the resonance region of pseudoscalar mesons, and discusses background suppression techniques for experimental measurements.

## Contribution

It extends previous measurements into the pseudoscalar resonance mass region and provides a detailed analysis of the photon-photon scattering cross section and background conditions.

## Key findings

- Elementary photon-photon scattering cross section calculated.
- Photon-photon scattering cross section in Pb-Pb derived from luminosity convolutions.
- Background from double π0 production analyzed and kinematic conditions proposed.

## Abstract

A study is presented to extend the measurements of photon-photon scattering in ultra-peripheral Pb-Pb collisions at the LHC into the mass region of the pseudoscalar resonances $\eta$ and $\eta'$. The elementary photon-photon scattering cross section is presented. The cross section for photon-photon scattering in Pb-Pb is derived by convoluting the elementary photon-photon cross section with the Pb-Pb photon luminosity. The main background to two-photon final states, arising from double $\pi^{0}$ production with two of the four decay photons escaping detection, is examined, and possible kinematical conditions are discussed to optimize the signal-to-background ratio for such measurements at mid-rapidity.