Targeting Natural Supersymmetry With Top Quarks

Thumbnail Image
Degree type
Doctor of Philosophy (PhD)
Graduate group
Physics & Astronomy
Grant number
Copyright date
Related resources

This thesis describes a search for natural supersymmetry via the production of light top squarks (stops) with the ATLAS experiment, using 13 TeV proton-proton collision data delivered by the Large Hadron Collider. A range of models is considered where the stop may decay to top quarks, b jets, and a variety of other supersymmetric particles. Stop masses as large as 950 GeV are excluded at 95% confidence level when decaying to a top quark and massless lightest supersymmetric particle (LSP). In scenarios where the LSP is a Higgsino, exclusions vary from 600 to 900 GeV depending on the relative stop branching fractions and Higgsino mass splitting. The impact of precision top-quark measurements on future searches is also discussed, including a measurement of quantum interference in top-quark production and measurement of the top-quark width. A differential mass distribution is measured in events with two charged leptons and two b-tagged jets that is sensitive to the interference property. The measurement is unfolded to particle level and the data are compared to state-of-the-art Monte Carlo predictions, which are found to describe the data well. A new technique is proposed to utilize this dataset to extract a value of the top-quark width, inspired by recent efforts to measure the Higgs boson width using off-shell decays. A value of 1.28 ± 0.27(exp.)±0.15(theory) GeV is extracted from the ATLAS data, in good agreement with the standard model prediction. Finally, a new hardware tracking system is described for use in the upgraded ATLAS Trigger system for the high-luminosity run of the LHC.

Elliot Lipeles
Date of degree
Date Range for Data Collection (Start Date)
Date Range for Data Collection (End Date)
Digital Object Identifier
Series name and number
Volume number
Issue number
Publisher DOI
Journal Issue
Recommended citation