Light-by-Light Scattering and Axion Like-Particle Searches in Pb+Pb Collisions at √sNN = 5:02 TeV in ATLAS Experiment at LHC

K. Maj, I. Grabowska-Bołd,  ATLAS Collaboration AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Kraków, Poland

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The ultra-peripheral Pb+Pb collisions at √sNN=5.02 TeV recorded by the ATLAS experiment are used to study a rare light-by-light scattering process, γγ→γγ, allowed in quantum electrodynamics via a loop diagram. The report summarises recent light-by-light measurements conducted using a combination of 2015 and 2018 Pb+Pb data sets collected by the ATLAS experiment, corresponding to an integrated luminosity of 2.2 nb-1. The light-by-light event candidates are required to consist of only two photons produced exclusively, each with transverse energy ET>2.5 GeV, pseudorapidity |η|<2.4, diphoton invariant mass mγγ>5 GeV, and with diphoton transverse momentum pTγγ<1 GeV and acoplanarity below 0.01. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles.

DOI:10.12693/APhysPolA.139.422 topics: light-by-light scattering, axion-like particles, ATLAS