In this thesis, the search for the production of the Higgs boson in associationwith two top quarks is presented. The main focus of this work is on the analysis optimised for the decay of the Higgs boson to a b-quark pair. The analysis is performed using 36.1 fbâ1 of ppcollision data at a centre of mass energy sqrt(s)=13 TeV collected by the ATLAS detector at the Large Hadron Collider during 2015 and 2016. The signal strength of ttH in relation to the Standard Model prediction for a Higgs boson with a mass of 125 GeV is measured to be mu(ttH) = 0.87 +0.64â0.61, with signal strengths greater than 2.0 excluded at the 95% confidence level. The combination of this analysis with searches targeting additional Higgs boson decay modes is subsequently presented. The measured signal strength in relation to the Standard Model prediction is mu(ttH) = 1.2 +/-0.3. This correspondsto an observed (expected) significance for ttH of 4.2sigma (3.8sigma), constituting evidence for the ttH production mode. Finally, a study into the ability to observe and model the colour connection of b-quarks in ttH(bb) and ttbar+jets events is presented. The jet pull angle observable is used to investigate the effect of colour connection on jet substructure. Such an observable is found to be sensitive to the underlying colour structure in events, showing differences between b-quarks which decay from a colour singlet in comparison to a colour octet. However, the effect is found to be small and a larger dataset is required to measure the effect in ttH events.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:748033 |
| Date | January 2018 |
| Creators | Raine, John |
| Publisher | University of Manchester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://www.research.manchester.ac.uk/portal/en/theses/evidence-for-the-production-of-a-higgs-boson-in-association-with-two-top-quarks-with-the-atlas-detector(8c0c9d01-ee21-4f7e-9db6-1f5d92de1faf).html |
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