A search for flavor changing neutral currents involving a top quark and a Higgs boson with the CMS experiment

Abstract

Slnce the disoovery of the Higgs boson in 2012 by !he ATLAS a.nd CMS experiments, Lhe Standard Model of elementary partiele physics is completely validaled at Electroweak scales. However, many phenomena are yet unexplained by the Standard Model, such as tlile existence of dark matter and dark energy. All in all, the Standard Modelis able to account for only 4% of the universe's energy oontent.

In this thesis. FCNC are investlgated in high-energy proton-pr·oton collislons at a center-of-mass energy of 13 TeV, produoed by the Large HadronCollider (LHC) and recorded by tihe CMS experiment at CERNin 2016 with an integrated luminosity of 36/fb.More specifically Lhe coupling of top quarks (t) to up (u) or charm (c) quarks and a Higgs boson (H), decaying into a pair of bottorn quarks, is investigated. By means of kinematic event reoonstructions, event categorisations and machine leaming techniques, an optimal disCi'imination power between the signal processes and Standard Modelbackground processas is obtained. The most stringent limits to date· are set on these processes, with expected (observed) upper
limits at 95% oonfidence level on the branching ratios of B(t ----. uH) !5;,
0.34% (0.44%) a.nd B(t--+ eH)0.47% (0.47%).

Date of Award	15 Sep 2017
Original language	English
Awarding Institution	Physics
Supervisor	Jorgen D'Hondt (Promotor), Kirill Skovpen (Co-promotor), Nicolaas Van Eijndhoven (Jury), Alberto Mariotti (Jury), Nathalie Vermeulen (Jury), Pascal Vanlaer (Jury) & N. Castro (Jury)