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Title: Higgs boson decays to b-bbar with associated t-quarks with the ATLAS detector at the Large Hadron Collider
Author: Al-Shehri, Azzah
ISNI:       0000 0004 7427 387X
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2018
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This thesis uses 32.88 1/fb of pp collision data gathered at the LHC by the ATLAS detector during 2016 at center of mass energy 13 TeV. The analysis employs kinematic fitting techniques by applying the KLFitter package on the signal-rich region using only the 6 jets selection mode (kB6). It construction variables providing good separation between signal and background in the search for ttH(H decay to b-barb) in the single-lepton final state (electron or muon). The scalar sum of transverse momenta is the variable of choice for the fit in signal-depleted regions. Using Boosted Decision Trees in the fit of signal-rich regions, a 95% CLs exclusion limit (significance) of 5.4 (4.25 \sigma) is obtained, with the corresponding ratio of the measured ttH signal cross-section to the Standard Model expectation of 3.69(+0.98,-0.88). This result indicates that there is an excess of events above the background expectation for the SM Higgs boson with mass of 125 GeV. The excess is even greater than the SM would predict (signal strength equal to 1). This excess over the SM prediction could be interpreted as a statistical fluctuation, and is not significant. More data would likely moderate this statistical aberration.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB Astronomy ; QC Physics