Seaching For A Charged Higgs Boson And Development Of A Hardware Track Trigger With The Atlas Experiment

Searching for a Charged Higgs Boson and Development of a Hardware Track Trigger with the ATLAS Experiment

Seaching for a Charged Higgs Boson and Development of a Hardware Track Trigger with the ATLAS Experiment

In 2012 the ATLAS and CMS experiments announced the discoveryof a new particle, a Higgs boson. This particle was hypothesized in the1960's and explains how fundamental particles get their mass. However, amodel with a single Higgs boson is still not able to explain the aforemen-tioned cosmological observations. An electrically charged Higgs boson isa feature of many suggested extensions of the current model, includingsupersymmetry. The properties of such a particle, e.g. its mass and howit interacts with other particles are not fixed by theory but forms a pa-rameter space in which we must look for it. Searches for charged Higgsbosons have been performed prior to the LHC, but with the new energyscale of the LHC, the experiments have been able to look for heavier par-ticles. In this work we searched for a charged Higgs boson decaying intothe heaviest two quarks, a top and bottom pair. No deviations from thestandard model were found in the data gathered up until 2016, and hencewe can set upper limits on the production rate of a charged Higgs boson.These limits can then be used to exclude parts of the parameter space.The LHC will be upgraded around 2025 to increase the luminosity,that is the intensity of the proton beams. Protons are not acceleratedone by one at the LHC but in bunches. The luminosity can be increasedby using more protons per bunch but also by squeezing the bunches to besmaller at the point of collision. This means that the rate at which we canhope to produce rare events will increase but also that the backgroundrates and so called pile-up, the number of proton collisions per bunchcrossing, will increase. The rate of bunch crossings at the LHC is muchtoo high for ATLAS to be able to readout and store all data for eachevent, instead we use triggers that select events which look interesting.The current triggers are not suited for the high rates and pile-up of theHigh Luminosity (HL) LHC after the upgrade and must thus be improved.A way to do this is to use the information from the tracking detector thatprovides information on the trajectories of charged particles. By usingalgorithms that can be implemented in hardware a track trigger can bemade fast enough to work within the short latency required at the HL-LHC. The tracking detector provides space points, measurements of theparticle trajectories at different intervals, to which a track can be fitted.The amount of data from the tracker is very large, and performing trackfits on all the combinations of the space point would take too much time.Therefore a track trigger must be able to select a subset of space points onwhich to perform the track fit. For this thesis we have explored the idea ofusing standalone electron and muon triggers to select a part of the trackervolume, and then select space points that match precomputed patternsthat correspond to high energy particles. It has been shown that this isa viable option to reduce background rates while keeping high efficiencyfor the events we want to keep, even in high pile-up conditions.

Search for Higgs Boson Decays to Charm Quarks with the ATLAS Experiment and Development of Novel Silicon Pixel Detectors

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.