Searching for Four Top Quarks with the ATLAS Detector

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.Thesis (MPhil) -- University of Adelaide, School of Physical Sciences, 202

The ABC130 barrel module prototyping programme for the ATLAS strip tracker

For the Phase-II Upgrade of the ATLAS Detector, its Inner Detector, consisting of silicon pixel, silicon strip and transition radiation sub-detectors, will be replaced with an all new 100 % silicon tracker, composed of a pixel tracker at inner radii and a strip tracker at outer radii. The future ATLAS strip tracker will include 11,000 silicon sensor modules in the central region (barrel) and 7,000 modules in the forward region (end-caps), which are foreseen to be constructed over a period of 3.5 years. The construction of each module consists of a series of assembly and quality control steps, which were engineered to be identical for all production sites. In order to develop the tooling and procedures for assembly and testing of these modules, two series of major prototyping programs were conducted: an early program using readout chips designed using a 250 nm fabrication process (ABCN-25) and a subsequent program using a follow-up chip set made using 130 nm processing (ABC130 and HCC130 chips). This second generation of readout chips was used for an extensive prototyping program that produced around 100 barrel-type modules and contributed significantly to the development of the final module layout. This paper gives an overview of the components used in ABC130 barrel modules, their assembly procedure and findings resulting from their tests.Comment: 82 pages, 66 figure

Searches for BSM physics using challenging and long-lived signatures with the ATLAS detector

Various theories beyond the Standard Model predict new, long-lived particles with unique signatures which are difficult to reconstruct and for which estimating the background rates is also a challenge. Signatures from displaced and/or delayed decays anywhere from the inner detector to the muon spectrometer, as well as those of new particles with fractional or multiple values of the charge of the electron or high mass stable charged particles are all examples of experimentally demanding signatures. The talk will focus on the most recent results using 13 TeV pp collision data collected by the ATLAS detector

Challenges of Measuring Graduation in Rwanda

Rwanda demonstrates how a process of community consultation and participation is able to identify and rank community members according to ‘social poverty’, drawing on the Ubudehe tradition which is considered a strength of Rwanda's social fabric. However, with the Ubudehe categorisation now the basis for determining eligibility to a range of social benefits, the process has come under some strain. This article highlights two issues related to targeting and graduation: (1) the difficulty in identifying the poor/non?poor and ranking the population using community participatory techniques; and (2) the sensitivity of eligibility criteria and graduation thresholds to different targeting modalities. Our primary interest is to establish whether improvements for identifying the poor and non?poor can be made without undermining community ownership and what these improvements would look like. This will be useful for policymakers in Rwanda as the new five?year development strategy places importance on graduating households out of extreme poverty