Luminosity Measurements with the ATLAS Inner Detector in Run 3 of the LHC

Luminosity is a fundamental parameter in any particle collider, linking measured event rates to cross sections of physics processes. In this contribution, the key ingredients of the ATLAS luminosity determination are outlined, with a focus on measurements performed with the Inner Detector in Run 3 of the LHC. The performance of the well-established track-counting algorithm is discussed, together with the results of the track-counting-based luminosity correction procedure applied in standard data-taking conditions. Alongside track counting, the initial development of a novel algorithm, measuring luminosity by counting clusters in the Pixel Detector, is presented. The optimisation of the cluster selection for luminosity measurements is discussed, together with preliminary studies of the algorithm performance and background characterisation.