# Initial Stages 2021

Jan 10 – 15, 2021
Weizmann Institute of Science
Asia/Jerusalem timezone
See you at IS2023 in Copenhagen in June 2023

## Light-by-light scattering in ultra-peripheral Pb+Pb collisions in the ATLAS experiment

Jan 12, 2021, 7:40 PM
1h 30m
Patio (vDLCC)

### Patio

#### vDLCC

bullet talk (poster) The initial stages of heavy-ion collisions

### Speaker

Agnieszka Ewa Ogrodnik (AGH University of Science and Technology (PL))

### Description

The ultra-peripheral Pb+Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV performed at the ATLAS experiment are used to
study a rare light-by-light scattering process, $\gamma\gamma\rightarrow\gamma\gamma$, allowed in Quantum Electrodynamics via a loop diagram.
The poster summarises recent light-by-light measurements conducted using a combination of 2015 and 2018 datasets recorded by the ATLAS experiment,
corresponding to an integrated luminosity of 2.2 n$b^{-1}$.
The light-by-light event candidates are required to consist of only two photons produced exclusively, each with transverse energy
$E_{\mathrm{T}} >$ 2.5 GeV, pseudorapidity $|\eta| <2.4$, diphoton invariant mass $m_{\gamma\gamma} > 5$ GeV,
and with diphoton transverse momentum $p_{\mathrm{T}^{\gamma\gamma}}$ < 1 GeV and acoplanarity below 0.01.
The differential distributions, presented as functions of kinematic and angular variables of the final-state photons, are unfolded for detector effects.
The fiducial and differential cross-sections are presented and compared with theoretical predictions.
The diphoton invariant mass distribution is used to set limits on the production of axion-like particles.

### Primary author

Agnieszka Ewa Ogrodnik (AGH University of Science and Technology (PL))