Observation of $\gamma\gamma\to\tau\tau$ in Pb+Pb collisions and constraints on the $\tau$-lepton $g-2$ with the ATLAS detector

This talk reports the observation of $\tau$-lepton pair production in ultraperipheral lead-lead collisions and a measurement of the $\tau$-lepton anomalous magnetic moment, $a_\tau$. The dataset corresponds to an integrated luminosity of 1.44/nb of Pb+Pb collisions at 5.02 TeV recorded by the ATLAS experiment in 2018.