A new spin on top-quark physics: using angular distributions to probe top-quark properties, and make the first observation of entanglement between quarks

Simpson, Ethan Lewis (2024) A new spin on top-quark physics: using angular distributions to probe top-quark properties, and make the first observation of entanglement between quarks. PhD thesis, University of Glasgow.

Abstract

Measurements of angular properties of top-quarks constitute stringent tests of the Standard Model, probe physics beyond it, and even reveal underlying quantum information phenomena. This thesis discusses angular top-quark properties in two new contexts. A study of tt¯ spin correlations and top-quark polarisations in associated tt¯Z production presents theoretical predictions for these parameters at √s = 13TeV. A measurement strategy for observation of spin correlations in tt¯Z production at the Large Hadron Collider is proposed, and the constraint on effective field theory models provided by angular observables investigated. Related angular observables are used to make the first ever observation of quantum entanglement between quarks, in the di-leptonic tt¯ -production channel. An entanglement marker D is extracted from an angular differential cross-section measured in ATLAS √s = 13TeV proton-proton collision data, and corrected to a fiducial particle-level phase-space. This observed entanglement marker is found to be −0.547 ±0.022, corresponding to an exclusion of the no-entanglement hypothesis well in excess of five standard deviations. Short studies on novel methods to emulate the ATLAS detector response are also presented.

• 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
• Supervisor's Name: Howarth, Dr. James
• Date of Award: 2024
• Depositing User: Theses Team
• Unique ID: glathesis:2024-84277
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 29 Apr 2024 14:11
• Last Modified: 29 Apr 2024 14:22
• Thesis DOI: 10.5525/gla.thesis.84277
• URI: https://theses.gla.ac.uk/id/eprint/84277