Looking for lepton flavour violation with the ATLAS detector: a search for Z → τl decays

In this thesis charged lepton flavour violation is researched. Chapter 1 starts with a theoretical introduction to lepton flavour violation in the Standard Model, and predictions for it from new physics models. Then in chapter 2, the technical design of the Large Hadron Collider and the ATLAS detector is summarised, which provides a basic understanding of how the proton beams are created and how the produced particles from their collision are detected. Subsequently, chapter 3 provides the details of the detector performance in reconstructing and identifying the particles that are used in the search for Z → lτ decays, as well as the several Standard Model processes that act as a background. In chapter 4 the constructed measurement model is discussed: a binned likelihood model with the invariant mass of the Z boson as the discriminating variable. Finally, the last chapter gives the unblinded results of the search, using the proton collisions recorded by the ATLAS experiment which totals a recorded luminosity of L = 20.3 fb⁻¹.