A search for tWZ production at the ATLAS experiment

Veltman, Alexander

A search for tWZ production at the ATLAS experiment

Thesis / Dissertation

2024

Publisher

University of Cape Town

Department

Department of Physics

Faculty

Faculty of Science

Abstract

The production of a single top quark in association with a W boson and a W boson (tWZ) is a rare Standard Model process that has never before been observed. The tWZ process will be a useful input into global Standard Model Effective Field Theory (SMEFT) fits due to its sensitivity to top-electroweak SMEFT coefficients in regions of high boson and boson transverse momenta. The process is also a relevant background in other top quark related measurements, such as the ttZ¯ cross section measurement. In this thesis, a search was performed for tWZ production using 140 fb−1 of √ s=13 TeV proton-proton collision data measured using the ATLAS detector. The search targets the trilepton and tetralepton final states, where regions were defined using physics object multiplicities. Graph neural networks were employed to perform signal-background discrimination. The signal strength of tWZ production µtWZ was extracted using a profile likelihood fit with a full systematic model describing experimental and modelling uncertainties. Blinded measurements of µtWZ are shown for each decay channel using an Asimov dataset as well as a combined signal extraction across both channels. The expected significance for the measurement of tWZ was determined to be 1.34σ where the precision of the measurement was limited by both systematic and statistical sources of uncertainty. Estimations for the measurements of µtWZ for higher luminosity datasets were also investigated

Keywords

tWZ

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