Recent results from ultra-peripheral lead-lead collisions with ATLAS

Abstract

Relativistic heavy-ion beams at the LHC are accompanied by a large flux of equivalent photons, leading to multiple photon-induced processes.
This report presents a series of measurements of such processes performed by the ATLAS Collaboration. Measurements of exclusive dilepton production (electron, muon, and tau pairs) are discussed. These processes provide strong constraints on the nuclear photon flux and its dependence on the impact parameter and photon energy. In particular, measurements of the cross-sections in the presence of forward neutrons provide an additional experimental handle on the impact parameter range sampled in the observed events. Furthermore, the tau-pair production measurements can constrain the anomalous magnetic dipole moment of the tau lepton. High statistics measurements of light-by-light scattering shown in this talk provide a precise and unique opportunity to investigate extensions of the Standard Model, such as the presence of axion-like particles. The measurement of charged hadron in photonuclear collisions using 5.02 TeV Pb+Pb data collected in 2018 by ATLAS is also discussed. The charged hadron particle yields are presented as a functions of pseudorapidity and transverse momentum in different categories of event multiplicity. Measurement of jet production in ultra-peripheral collisions performed with the ATLAS detector using high-statistics 2018 Pb+Pb data is presented.