Higgs boson decays to b-bbar with associated t-quarks with the ATLAS detector at the Large Hadron Collider

QB Astronomy;QC Physics

Al-Shehri, Azzah ; Doyle, Anthony

University:University of Glasgow

Department:School of Physics and Astronomy

关键词: QB Astronomy;    QC Physics;   

Others  :  http://theses.gla.ac.uk/30694/8/2018Al-ShehriPhD.pdf

来源: University of Glasgow

【 摘 要 】

This thesis uses 32.88 1/fb of pp collision data gathered at the LHC by the ATLAS detector during 2016 atcenter of mass energy 13 TeV. The analysis employskinematic fitting techniques by applying the KLFitter package on the signal-rich region using only the 6 jetsselection 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 of3.69(+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.