Boosting to the top: measurements of boosted top quarks and Higgs bosons with the ATLAS detector at the Large Hadron Collider

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$^{-1}$ of $\sqrt{s}$ of 13 TeV collected in 2015, is presented. Two kinematic properties of the boosted top quark, P$_{T}^{t,had}$ and y$^{t,had}$ are unfolded to a fiducial volume and compared to a number of state-of-the-art Monte Carlo simulations. Then,using 36 fb$^{−1}$ 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 emphasisis placed on the high $pT$ boosted channel, the first time such an analysis has been published by the ATLAS collaboration.