Luminosity Monitoring using $Z\rightarrow \ell \ell$ events at $\sqrt{s} = 13$~TeV with the ATLAS detector

During Run 2, the LHC delivered instantaneous luminosities of approximately $10^{34} cm^{-2} s{-1}$ at $\sqrt{s}=13$ TeV in $pp$ collisions. At such high instantanenous luminosities, measuring the decay rate of $Z\to\ell\ell$ provides a powerful tool to monitor the luminosity recorded by ATLAS~\cite{ATLAS} over time periods as short as 60s. These proceedings present an overview of the method, outlining the event selection, data-driven efficiency determination and corrections derived from simulation, as well as showcasing the robustness of the final results. The absolute luminosities obtained independently in both the $Z\to ee$ and $Z\to\mu\mu$ channels agree to within approximately 1\%, with an excellent stability of around 0.5\%, a non-trivial result considering both channels have their own distinct chain of corrections. The stability with respect to the baseline ATLAS luminosity measurement is evaluated, and found to be typically within 0.5\%.