Search for Higgs-Boson Production in Association with a Top-Quark Pair in the Boosted Regime with the CMS Experiment

In 2012, the last missing piece of the Standard Model of particle physics has been discovered by the ATLAS and CMS collaborations, the Higgs boson. Still, some production modes of this particle remain undiscovered to date. One of them is the Higgs-boson production in association with a top-quark pair (ttH). A special feature of this process is the direct access to one of the most important Higgs-boson properties: the top-Higgs Yukawa coupling. The small cross section of ttH production is one of the reasons, why this process still remains unobserved. Especially for a Higgs boson decaying into a bottom-quark pair, the irreducible background by top-quark pair production is overwhelming. A further challenge is the ambiguous assignment of jets to the numerous final-state particles in the reconstruction of the collision event. A solution to this problem is provided by the investigation of a phase space, where the massive particles feature large transverse momenta, the boosted regime. For this special case, the decay products of the massive particles are collimated and the original massive particles can be reconstructed and identified with the help of dedicated algorithms. ... mehrThis thesis presents the implementation, optimization, and execution of the boosted analysis strategy in a search for ttH production with a Higgs-boson decay into a bottom-quark pair and a semileptonic top-quark pair decay. The search is performed based on proton-proton collisions at a center-of-mass energy of √s = 13 TeV recorded with the CMS experiment in 2015. It represents the first search for ttH production with a Higgs-boson decay into a bottom-quark pair and a semileptonic top-quark pair decay at a center-of-mass energy of √s = 13 TeV. Further, this search features the first dedicated investigation of the boosted regime in the search for ttH production.