Measurement of Higgs couplings to top quarks and τ leptons with the ATLAS detector

Since the discovery of the Higgs boson in 2012 during the first run of the Large Hadron Collider (LHC) at CERN, extensive measurements have been performed to characterize its properties. Its mass, spin, parity and couplings have been studied in detail with no significant deviations from the SM predictions observed. The second run of the LHC saw incredible progress with the addition of new measurements. This thesis highlights the measurements of Higgs couplings to third generation fermions, first with the observation of the ttH process and then through improved pp → H → ττ cross section measurements. The search for the ttH process is discussed in the context of the ttH → multilepton analysis, with an emphasis on final states with τhad-vis. A ttH cross section measurement, obtained in combination with results from tt(H → γγ), tt(H → ZZ* → 4ℓ) and tt(H → bb), is also presented. All results are found to be compatible with the Standard Model predictions. The study of Higgs decays involving τ leptons is expanded upon with the measurement of the pp → H → ττ cross section using the full Run 2 dataset, and a new method to estimate the largest background to this measurement is introduced. The improvement in the precision of pp → H → ττ measurements coupled with an increased sensitivity to broader regions of phase space allows for a deeper scrutiny of the Standard Model predictions, with the theory still providing an accurate description of the experimental results.

Department dc:contributor.department

Physics

Year dc:date.issued

2021

Author dc:creator

• Ojeda, Martina Laura

Advisor dc:contributor.advisor

• Savard, Pierre

• ATLAS detector
• Higgs boson
• tau lepton

Handle dc:identifier.uri

http://hdl.handle.net/1807/109253

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/109253