Boosting to the Top : Measurements of Boosted Top Quarks and Higgs Bosons with the Atlas Detector at the Large Hadron Collider

• Main Author: Fenton, Michael
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Quarks

Between 2015 and 2018, proton-proton collisions were performed at the highest energy ever achieved in man-made particle accelerators, with the Large Hadron Collider at CERN. This thesis presents measurements performed with the ATLAS detector which fully exploit this energy, of the high momentum production of the most massive fundamental particles known to exist: the top quark and the Higgs boson. Firstly, the differential cross-section of highly boosted top quarks, measured in the lepton+jets channel using the 3.2fb of 13TeV collected in 2015, is presented. Two kinematic properties of the boosted top quark, pT and absolute rapidity, are unfolded to a fiducial volume and compared to a number of state-of-the-art Monte Carlo simulations. Then, using 36fb of data from 2015 and 2016, the search for associated production of a top quark pair with a Higgs boson decaying to a pair of bottom quarks is discussed. Particular emphasis is placed on the high pT boosted channel, the first time such an analysis has been published by the ATLAS collaboration. A limit of 2.0 times the Standard Model expectation is set on ttHbb production alone, which after combining with analyses in other channels leads to observation of both ttH production and Hbb decay. Finally, a number of optimisations of the boosted ttHbb analysis are presented, in view of a future publication of the combined ttHbb search using the full 140fb of data collected by the end of 2018.