51³Ô¹Ï

Topic

Effectively Exploring New Physics: A first EFT interpretation using the WZ→llvl process with the ATLAS detector at the LHC

Department of Physics and Astronomy

Date & location

• Wednesday, July 2, 2025
• 10:30 A.M.
• Clearihue Building, Room B017

Examining Committee

Supervisory Committee

• Dr. Robert McPherson, Department of Physics and Astronomy, 51³Ô¹Ï (Co-Supervisor)
• Dr. Richard Keeler, Department of Physics and Astronomy, UVic (Co-Supervisor)
• Dr. Isabel Trigger, Department of Physics and Astronomy, UVic (Member)
• Dr. Cornelia Bohne, Department of Chemistry, UVic (Outside Member)

External Examiner

• Dr. Simon Viel, Department of Physics, Carleton University

Chair of Oral Examination

• Dr. Nishant Mehta, Department of Computer Science, UVic

Abstract

The Standard Model (SM) of particle physics, while highly successful, has known limitations. The decoupling theorem and the effective principle guide Beyond the SM Physics research by allowing us to describe dynamics at relevant length scales without fully understanding smaller-scale interactions. The Standard Model Effective Field Theory (SMEFT) builds on these concepts, treating the SM as a low-energy approximation of a deeper, more fundamental theory. This fundamental theory introduces new heavy particles at a higher energy scale, Λ. By integrating out these beyond-the-Standard-Model (BSM) particles, SMEFT offers a model-independent way to describe their potential effects.

This thesis focuses on electroweak processes involving the coupling of the 𝑊 and 𝑍 bosons, where both bosons decay into leptonic final states. The data used to perform this analysis correspond to the full ATLAS Run-2 dataset, collected from 2015 to 2018, and correspond to an integrated luminosity of 139 fb⁻¹ and a centre-of-mass energy of √𝑠 = 13 TeV.

Multiple kinematic and angular observables are used to constrain the strength of ten SMEFT parameters that affect the 𝑊𝑍 channel. Additionally, the thesis includes a study of the interference between different EFT operators, which is a novel contribution to the 𝑊𝑍 channel. The results are interpreted in the context of comparing data with the SMEFT predictions and exclusion limits are set at 95% confidence level. No significant deviation from the Standard Model is observed for most of the 1D and 2D particle-level fits. Strong constraints on cW and cHj3 have been obtained across all observables.

These results provide a deeper understanding of potential deviations from the Standard Model and contribute to the ongoing search for new physics.