Measurement of the top-quark mass with the ATLAS detector using tt¯events with a boosted top quark

Watton, Elliot (2025) Measurement of the top-quark mass with the ATLAS detector using tt¯events with a boosted top quark. PhD thesis, University of Glasgow.

Abstract

As the heaviest fundamental particle observed to date, the top quark plays a crucial role in particle physics. Precise determination of its mass is essential for testing the internal consistency of the Standard Model and probing potential new physics. This thesis presents a
measurement of the top-quark mass using the full Run 2 dataset, corresponding to an integrated luminosity of 140 fb−1, collected during proton-proton collisions at a centre-of-mass energy of √s = 13 TeV by the ATLAS experiment at the Large Hadron Collider between 2015 and 2018. The analysis focuses on top-antitop-quark pair decays that produce a highly energetic top quark, reconstructed using a single large-radius jet. The average invariant mass of this jet is used to extract the top-quark mass using a profile likelihood fit, incorporating two additional observables to constrain and reduce systematic uncertainties. This approach yields the most precise top-quark mass measurement by ATLAS in a single channel to date: 172.95 ± 0.53 GeV. In addition, this thesis presents the development and integration of the Fast Track Finder algorithm into the ATLAS trigger system. This represents the first successful implementation of a CPU-based charged-particle track reconstruction chain within the ATLAS trigger that is intended for use during the operation of the High-Luminosity Large Hadron Collider, which is scheduled to commence in 2030.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: Q Science > QB Astronomy; Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Funder's Name: Science & Technologies Facilities Council (STFC)
• Supervisor's Name: Owen, Professor Mark
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85366
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 08 Aug 2025 10:35
• Last Modified: 08 Aug 2025 11:09
• Thesis DOI: 10.5525/gla.thesis.85366
• URI: https://theses.gla.ac.uk/id/eprint/85366