Light-by-light scattering in ultra-peripheral Pb+Pb collisionsat $\sqrt{s_{NN}}$ = 5.02 TeV with the ATLAS detector

Light-by-light scattering ($\gamma\gamma\rightarrow\gamma\gamma$) is a quantum-mechanical process that is forbidden in the classical theory of electrodynamics. This reaction is accessible at the Large Hadron Collider thanks to the large electromagnetic field strengths generated by ultra-relativistic colliding lead (Pb) ions. Using 480~\invmub~of Pb+Pb collision data recorded a at centre-of-mass energy per nucleon pair of $5.02$~TeV by the ATLAS detector, we report evidence for the $\gamma\gamma\rightarrow\gamma\gamma$ reaction. A total of $13$ candidate events are observed with a background expectation of $2.6\pm0.7$ events. After background subtraction and analysis corrections, the fiducial cross-section of the process $\textrm{Pb+Pb}\,(\gamma\gamma)\rightarrow \textrm{Pb}^{(\ast)}\textrm{+}\textrm{Pb}^{(\ast)}\,\gamma\gamma$ has been measured to be $70 \pm 24~\textrm{(stat.)} \pm 17~\textrm{(syst.)}$ nb, which is in agreement with the Standard Model predictions.