Legacy cross-section measurements of the $t\bar{t}Z$ production process in the trileptonic final state at $\sqrt{s}=13\,$TeV with the ATLAS detector
von Steffen Korn
Datum der mündl. Prüfung:2023-06-23
Erschienen:2024-01-31
Betreuer:Prof. Dr. Arnulf Quadt
Gutachter:Prof. Dr. Arnulf Quadt
Gutachter:Prof. Dr. Marı́a Moreno Llácer
Dateien
Name:Dissertation_Steffen_Korn_25-01-2024.pdf
Size:10.8Mb
Format:PDF
Zusammenfassung
Englisch
After three years of data-taking during the second run of the LHC at CERN, Geneva, Switzerland, the ATLAS detector has recorded its most extensive proton-proton collision data set to date, allowing for a wide range of Standard Model (SM) precision measurements. Through this dataset, a large number of top quark pairs in association with a Z boson ($t\bar{t}Z$) and with it key SM parameters are accessible. Several theories beyond the SM provide possible extensions to the electroweak sector of the SM, leading to deviations of the $t\bar{t}Z$ production cross-section from its SM predictions in the presence of new physics. With the large dataset recorded by ATLAS, a final $t\bar{t}Z$ analysis has gained interest to provide legacy cross-section measurements and interpretations within the SM effective field theory to provide the most cohesive picture of the $t\bar{t}Z$ production process to date. This work mainly presents the results of the inclusive cross-section measurement obtained using the $140\,\text{fb}^{-1}$ large Run2 dataset collected by the ATLAS detector between 2015 and 2018 at $13\,$TeV centre-of-mass energy. It focuses on the measurement of the inclusive cross-section in the trileptonic channel, where exactly three leptons (electrons or muons), two originating from a Z decay and one from a leptonic top quark decay and at least three jets, one of which must be b-tagged, are selected. The obtained data is unfolded using the profile-likelihood unfolding approach, and interpretations of the inclusive and differential measurements within the framework of the SM effective field theory are presented. A deeper focus of this thesis lies in developing neural-network-based classifiers for $t\bar{t}Z$ event classification in the trileptonic channel.
Keywords: High energy particle physics; ATLAS; Top Quark; Z Boson; CERN