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Title: A search for top-antitop quark resonances with the ATLAS detector at the LHC
Author: Duncan, Anna
ISNI:       0000 0004 7963 104X
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2019
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Various extensions to the Standard Model postulate the existence of heavy particles that decay to a top-antitop quark pair. If one of these particles exists with a mass of a few TeV then it may be produced during proton-proton collisions at the Large Hadron Collider (LHC). The analysis presented in this thesis searches 36 fb−1 of √s = 13 TeV proton- proton collision data collected by the ATLAS detector for evidence of a top-antitop quark resonance, and sets upper limits on the production cross section of new heavy particles in a set of benchmark models. The observed top-antitop quark invariant mass spectrum agrees well with the spectrum expected under the Standard Model and no evidence of a top-antitop quark resonance is found. A 1% width Z' boson in a topcolour-assisted technicolour model is observed to be excluded at masses below 3.0 TeV, a 30% (15%) width Kaluza-Klein gluon in a Randall-Sundrum model is observed to be excluded at masses below 3.7 TeV (3.8 TeV), and a 3-6% width Kaluza-Klein graviton in a Randall-Sundrum model is observed to be excluded in the mass interval 0.45 < mGKK < 0.65 TeV. Some techniques developed to improve the sensitivity of the analysis are described: a new method of electron-in-jet overlap removal and a reconstruction of semi-boosted and very boosted top-antitop quark decay topologies. A study evaluating the prospects of this search at the High Luminostiy LHC is also presented. It estimates that a search of 3000 fb−1 of proton-proton collision data collected using an upgraded ATLAS detector will be able to exclude a Z' boson at masses below 4 TeV.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: QC Physics