Electronic Theses and Dissertations (PhDs)

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Browsing Electronic Theses and Dissertations (PhDs) by Author "Mellado, Bruce"

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    Development of TileCoM firmware and software for the off-detector electronics of the ATLAS Tile Calorimeter at the HL-LHC
    (University of the Witwatersrand, Johannesburg, 2023-08) Gololo, Mpho Gift Doctor; Argos, Fernando Carrio; Mellado, Bruce
    In 2010 the LHC started to operate as the energy frontier particle accelerator in the world, situated close to Geneva and 100 m below the French and Swiss border in a circular tunnel of 27 km. The HL-LHC which is an upgrade of the LHC is envisioned to maximize the instantaneous luminosity of L = 1 × 1034 cm−2s −1 by a factor of 5 to fully exploit the physics potential at the energy frontier. During 10 years of operation, an improved TDAQ system architecture will have the capability to accommodate the trigger rates and the amount of data generated from the HL-LHC. TileCal is the ATLAS central hadronic calorimeter, a sampling calorimeter with iron as passive medium and plastic scintillator tiles as active medium. The ATLAS TileCal Phase-II upgrades will prepare the ATLAS experiment for the HL-LHC and includes new requirements in terms of radiation levels, an increase in data bandwidth, and clock distribution. To meet the requirements of the HL-LHC, a completely new readout electronics is designed to support the data acquisition system of TileCal. As part of the new readout electronics, this thesis is focused on the design of the TileCoM and Tile GbE Switch. The Tile GbE Switch PCB is manufactured by two South African companies, Trax Interconnect and Jemstech. The PCBs are fully func tional and have been integrated with new readout electronics. Three main function alities are implemented on the TileCoM in software and firmware implementation as key elements of the TDAQ and DCS of the ATLAS TileCal at the HL-LHC. The TileCoM and Tile GbE Switch are successfully integrated with the ATLAS Phase II TileCal upgrade electronics. This is achieved by successful remote control and monitoring of the ATLAS TileCal Phase-II upgrade electronics. This thesis shows monitoring results based on voltage, current and other parameters.
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    Search for new resonances in the four-lepton channel and implementation of the LED integrator panel for the PROMETEO system in the ATLAS Tile Calorimeter
    (University of the Witwatersrand, Johannesburg, 2024) Mtintsilana, Onesimo; Kumar, Mukesh; Mellado, Bruce
    The Large Hadron Collider (LHC) has transformed our understanding of fundamental particles and forces, notably with the seminal discovery of the Higgs boson in 2012, which completed the Standard Model (SM) of particle physics. Despite its success, the SM leaves numerous unanswered questions, motivating a quest for new physics. This thesis explores three main avenues: Firstly, it investigates the possibility of an extended Higgs sector or alternative SM extensions, focusing on heavy ZZ resonances that decay into four leptons. Using a dataset of 139 fb−1 from proton-proton collisions at the LHC, this study explores both gluon-gluon fusion and vector-boson fusion production mechanisms. Although no significant signal for a new resonance is observed, upper limits on the production cross section of spin-0 or spin-2 particles are established. These limits provide constraints on specific theoretical models, such as Type-I and Type-II two-Higgs doublet models for spin-0 resonances, and the Randall-Sundrum model for spin-2 resonances. Intriguingly, the combined results of ATLAS and CMS for Run 2 and Run 3 data in the final state of 4 leptons exhibit an excess around 250 GeV, reaching a significance of 2.4σ which is in the region of interest of the multi-lepton anomalies.. In the second part, the analysis extends to heavy boson decays resulting in a final state with four leptons, specifically focusing on the R boson or the A boson decays into a combination of the SM Higgs boson and another boson, denoted S, which further decays into dark-matter candidates. No evidence contradicting SM predictions is found, yielding stringent upper limits on the production cross-sections of these hypothesised bosons and their branching ratios at a 95% confidence level. Lastly, the thesis highlights advancements in Higgs boson studies and new particle discovery potential in the upcoming High-Luminosity LHC era starting in 2029, emphasising improvements to the ATLAS detector electronics, particularly the integration of a new LED Integrator Panel within the Prometeo portable readout module system, enabling precise calibration and monitoring of individual detector components
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    The application of weakly supervised learning in the search for heavy resonances at the LHC
    (University of the Witwatersrand, Johannesburg, 2023-06) Choma, Nalamotse Joshua; Ruan, Xifeng; Mellado, Bruce
    The discovery of the Higgs boson at the Large Hadron Collider by the ATLAS and CMS experiments has made the search for new physics beyond the Standard Model a priority in the field of High Energy Particle Physics. New resonances have yet to be discovered using inclusive and model-dependent searches, which means they may be driven by subtle topologies. Rapid improvements in Machine Learning techniques have led to their increasing application in High Energy Particle physics. Unlike supervised learning, which is known to assume full knowledge of the underlying model, semi-supervised learning, in particular weakly supervised learning, allows the extraction of new information from data with partial knowledge. The goal of this study is to set up searches for heavy resonances at the electroweak scale with topological requirements performed in both inclusive and exclusive regions of phase-space tailored to a particular production mode. These resonances could be generated with different production mechanisms. In this work, we describe search procedures based on weakly supervised learning applied to mixed samples and used to search for resonances with little or no prior knowledge of the production mechanism. This approach has the advantage that sidebands or control regions can be used to effectively model backgrounds without relying on models. The effectiveness of this method is measured by the production of the Standard Model Higgs boson, which decays into a pair of photons in both inclusive and exclusive regions of phase-space at the LHC. Having confirmed the ability of the method to extract various Standard Model Higgs boson signal processes, the search for new phenomena in high mass final states will be set up at the LHC. Subsequently, the approach is used in the search for new resonances in the Zγ final state with Z → e +e − or Z → µ +µ −, using the Monte Carlo simulated signal samples for 139 fb−1 of integrated luminosity for Run 2 collected at the LHC. The weakly supervised learning approach is implemented and compared to the performance of the fully supervised approach, which is then used to calculate the production limit for Higgs-like particles for Zγ where the significance of the signal is maximal.