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The Higgs: A colored View from the Top at ATLAS

Final Report Summary - COLORTTH (The Higgs: A colored View from the Top at ATLAS)

The project "COLORTTH" had two main aims. One aim was the development and study of QCD colour flow variables in top-antitop quark (ttbar) processes, and the second goal was the first measurement of the top-Higgs Yukawa coupling. Both goals have been reached fully. The QCD colour flow has been studied in top quark decays, using proton-proton collision data from the ATLAS experiment at the large hadron collider (LHC) at CERN. Data at centre-of-mass energies of 8 and 13TeV has been analysed.

A clear sensitivity of the observable to QCD colour flow could be seen. In 2018, the first observation of the associated production of the Higgs boson with two top quarks (ttH) was reported. This process allows the direct extraction of the top-Higgs Yukawa coupling. In this project, dileptonic final states for ttH, with the Higgs decaying into two b-quarks, have been studied. Novel techniques on reconstructing the relevant final state were developed. This was then further used in searches for heavy charged Higgs bosons of two-Higgs-doublet models, enabling unprecendented sensitivity.

Furthermore, as part of the project differential distributions of observables in ttbar-dominated events have been measured, which are used to compare theory to prediction and tune Monte Carlo simulators.A phenomenological study of heavy charged Higgs bosons in maximally symmetric two-Higgs-doublet models has been performed, showing how improved analysis techniques can yield higher sensitivities than reached so far. In addition, a study of boosted top tagging has been published.

Since the start of the "COLORTTH" project in 2014, further insights into the fundamental laws of nature have been reached. The impact of the measurements and methods go beyond the end of the project.