A precise measurement of the luminosity is an essential part of the ATLAS physics program and is of particular importance to cross-section measurements, where it can be one of the largest systematic uncertainties. The track-counting method is one of several approaches used within ATLAS to compute the luminosity and involves counting the number of charged-particle tracks reconstructed in the Inner Detector. The average number of tracks scales linearly with the number of simultaneous proton-proton interactions, µ, per bunch-crossing, and can therefore be used to measure the luminosity.
This poster presents studies of the long term stability of the track-counting luminosity measurement in the LHC Run 2. Different track selection criteria are studied and are compared on a run-by-run basis, providing insights on changing detector conditions and beam configurations throughout each data-taking year. In addition, events from Z—>µµ decays are used to test the efficiency of the track selections and to study the stability over time.