Observation of Light-by-Light scattering in ATLAS

These proceedings describe the observation of the light-by-light scattering process, $\gamma\gamma\rightarrow\gamma\gamma$, in Pb+Pb collisions at $\sqrt{s_\textrm{NN}} = 5.02\,\TeV$. The analysis is conducted using a data sample corresponding to an integrated luminosity of $1.73\,\inb$ collected in November 2018 by the ATLAS experiment at the LHC. After event selection 59 candidate events are observed for a background expectation of $12 \pm 3$ events. This establishes the $\gamma\gamma\rightarrow\gamma\gamma$ process with an observed significance of 8.2 standard deviations. The measured fiducial cross section is $78 \pm 13 \textrm{(stat.)} \pm 7 \textrm{(syst.)} \pm 3 \textrm{(lumi.)} \,\textrm{nb}$.