Searching for Four Top Quarks with the ATLAS Detector

Abstract

The Standard Model predicts the existence of events containing four top quarks, but as yet they have not been experimentally observed. Here, the work focuses on events containing two same-sign leptons, or three leptons. This thesis explores the methods used to look for evidence for the Four Top Standard Model process at the ATLAS detector, at CERN. The optimisation of Boosted Decision Tree algorithms is performed using a multivariate analysis, with the aim of extracting a statistically significant signal strength. To date, the analysis data is still blinded, and as such the final results are not yet available. The four top process is especially interesting because of its relevance to Beyond Standard Model physics relating to the Higgs boson. In addition, planned upgrades to the ATLAS Inner Tracker subsystem – the Pixel Detector in particular – are discussed with reference to the work being undertaken at the University of Adelaide. These upgrades will allow the University to contribute to the ongoing upgrade work being done on ATLAS by providing an environment where newly built Inner Tracker modules can be tested before they are placed in the detector.