This book explores the Higgs boson and its interactions with fermions, as well as the detector technologies used to measure it. The Standard Model of Particle Physics has been a groundbreaking theory in our understanding of the fundamental properties of the universe, but it is incomplete, and there are significant hints which require new physics. The discovery of the Higgs boson in 2012 was a substantial confirmation of the Standard Model, but many of its decay modes remain elusive. This book presents the latest search for Higgs boson decays into c-quarks using a proton-proton collision dataset collected by the ATLAS experiment at the Large Hadron Collider (LHC). This decay mode has yet to be observed and requires advanced machine learning algorithms to identify c-quarks in the experiment. The results provide an upper limit on the rate of Higgs boson decays to c-quarks and a direct measurement of the Higgs boson coupling strength to c-quarks. The book also discusses the future of particle physics and the need for significant improvements to the detector to cope with increased radiation damage and higher data rates at the High-Luminosity LHC. It presents the characterization of the ATLAS pixel detector readout chip for the inner detector upgrade (ITk). The chip was subjected to irradiations using X-rays and protons to simulate the radiation environment at the HL-LHC. The tests showed that all readout chip components, including the digital logic and analogue front-end, are sufficiently radiation-tolerant to withstand the expected radiation dose. Finally, this book describes monolithic pixel detectors as a possible technology for future pixel detectors. This book is ideal for individuals interested in exploring particle physics, the Higgs boson, and the development of silicon pixel detectors.

In this thesis, searches for the exclusive Standard Model (SM) and charged hMSSM Higgs bosons are performed. While observations of the SM Higgs boson in 2012 by ATLAS and CMS collaborations were ground-breaking, several of the SM Higgs boson properties such as its coupling strengths and branching ratios of its decays still carry large systematic uncertainties. Higgs boson candidates from exclusive production could lower these systematic uncertainties due to their cleaner production environment, improving knowledge of the SM Higgs boson sector. Since the charged Higgs boson is not included in the SM, its evidence would clearly indicate physics beyond the SM which could address the hierarchy problem. Since no signal is observed for either of these bosons, limits to their production cross sections are set. A 95% confidence-level upper limit on the total production cross-section for exclusive Higgs boson is set to 1.2 pb. Limits on the total production cross section of the charged Higgs boson times its branching ratio to [T V] are set between 1.9 pb and 15 fb, for charged Higgs boson masses ranging from 200 to 2000 GeV.

This thesis presents a search for invisible decays of the Higgs boson using the vector boson fusion channel. This uses 36 fb-1 of proton-proton collision data at [square root] s = 13 TeV using the ATLAS detector at the Large Hadron Collider. The experimental methods for understanding the signal and background processes as well as detector effects are described in detail. The search is carried out in several regions defined by kinematic requirements on the final-state objects, and the observed event yields are used in a profile-likelihood fit in order to constrain the backgrounds. The results are interpreted using a modified frequentist method and are found to be consistent with the Standard Model expectations. An upper limit of 34% (28% expected) at 95% C.L. is placed on the invisible branching ratio of the Higgs boson. Re-interpretation of these results in terms of dark matter is also discussed, in the context of the Higgs portal and other simplified models.