A Search for the H mm Decay and a Measurement of the Mass of the Higgs Boson using H- 4l Events with 139 fb-1 of Proton-proton Collision Data Collected by the ATLAS Experiment

Using a dataset collected with the ATLAS detector during run-2 of the Large Hadron Collider, a search for the decay of the Higgs boson to two muons and a measurement of its mass are presented. Common to both measurements, an overview of the theoretical background, the Large Hadron Collider, the ATLAS experiment and particle reconstruction algorithms is provided. When the work in this thesis was performed, no evidence for the H ! μμ decay had been observed. The search presented in this thesis uses multivariate classification algorithms to classify events and maximize the expected statistical significance of the result. A signal excess of 2.0 was measured when testing the background-only (no H ! μμ) hypothesis and the signal strength was found to be in agreement with the Standard Model prediction, to within statistical and systematic uncertainties. The measurement of the Higgs boson’s mass was performed using H ! 4l events. Although the measurement of the Higgs boson’s mass has been performed in the same channel by the ATLAS collaboration in the past, the run-2 dataset used in this thesis is approximately four times larger than before, which is expected to reduce the uncertainty by a factor of two. The measurement uses multivariate machine learning techniques to discriminate signal and background events and exploit the inhomogeneous resolution of the ATLAS detector. The measurement is yet to be performed on data, but the expected uncertainty is ± 0.19 (± 0.18 Stat only) GeV.

Department dc:contributor.department

Physics

Year dc:date.issued

2022

Author dc:creator

• Adamek, Lukas

Advisor dc:contributor.advisor

• Savard, Pierre

• ATLAS Detector
• Higgs boson
• Large Hadron Collider

Statement dc:rights

• Attribution-NonCommercial 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc/4.0/

Handle dc:identifier.uri

http://hdl.handle.net/1807/110721

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/110721