Precision measurements of the Higgs boson's properties are a powerful tool to look for deviations from the predictions of the Standard Model (SM) of particle physics. The 139/fb of proton-proton collision data which have been collected by the ATLAS experiment during Run 2 of the LHC, offer an opportunity to investigate rare Higgs-boson topologies, which are particularly sensitive to new physics scenarios but experimentally difficult to access. Several such measurements, which target Higgs-boson decays to heavy-flavour quarks, as well as their combinations are presented in this thesis. A novel analysis that measures Higgs-boson production in association with a heavy vector boson V (VH, with V=W,Z) at high energies is presented. Dedicated Higgs-boson reconstruction techniques are applied to reconstruct the highly Lorentz-boosted Higgs-boson decays into pairs of bottom quarks. The measurement is subsequently combined with a VH cross-section measurement at low and intermediate pT(V) to provide a differential cross-section measurement in kinematic fiducial volumes over the largest possible pT(V) range. All cross-section measurements agree with the SM predictions within relative uncertainties that range from 30% to 300%. The results are furthermore interpreted as limits on the parameters of a SM effective field theory. Finally, a combination of measurements of Higgs decays to heavy-flavour quarks is used to experimentally determine that the Higgs-boson coupling to charm quarks is weaker than to bottom quarks, as predicted by the SM. The target audience for the thesis are physicists and physics students, in particular those with a background in high energy physics.

Auteur

I am an experimental particle physicist currently working at the European Laboratory for Particle Physics, CERN. Originally from the city of Elzach in Germany, I studied physics at the University of Freiburg where I obtained both my bachelors and masters degree. During this time I came into contact with the ATLAS experiment at the Large Hadron Collider (LHC) through my thesis projects which I performed in the group of Prof. Dr. Karl Jakobs. After I spend the summer of 2016 at CERN as a summer student to work on beam test studies with silicon strip modules for the planned upgrade of the ATLAS detector, I made the decision to pursue a career in experimental high energy physics. For my Ph.D. I moved to the Dutch National Institute for Particle Physics (Nikhef), where I performed the work that is summarized in the proposed book under the supervision of Prof. Dr. Wouter Verkerke and Dr. Tristan du Pree. My Ph.D. was awarded with the highest 'cum laude' distinction in the Netherlands, and mythesis won the ATLAS thesis award in 2023. So far, my research was and is performed within the ATLAS collaboration and focuses on precise measurements of the Higgs boson, as well as on the upgrade of the ATLAS silicon tracking detector towards the High-Luminosity LHC.