Search for Charged Higgs through a Reinterpretation of a Dark Meson Search with the ATLAS Experiment Based on 140 fb$^{-1}$ of LHC $ \sqrt{s} = 13$ TeV Proton-Proton Collisions

This thesis presents a search for single charged Higgs production through a reinterpretation of an existing Dark Meson search. The data used in the analysis is recorded by the ATLAS experiment at the Large Hadron Collider (LHC) during Run 2 with an integrated luminosity of 140 fb$^{-1}$. The LHC is a particle accelerator located in Geneva, Switzerland that collides two beams of protons. ATLAS is one of the four detectors that measures collisions delivered by the LHC.

    The discovery of the neutral Higgs Boson of mass 125 GeV by the ATLAS and CMS experiments in 2012 prompted discussions on whether extensions of the Standard Model (SM) scalar sector exist. The two-Higgs-doublet model (2HDM) is one of the simplest extensions to the SM that predicts the existence of charged Higgs.

    A reinterpretation is an analysis method commonly used in High energy Physics to speed up the search process, when certain conditions apply. Different theory models often share similar experimental signatures for signals as well as background processes. It is therefore possible to recycle a previously established analysis for a new signal. In this thesis, the search for dark meson is used to search for a different hypothetical particle, the charged Higgs predicted in 2HDM.
    
    The search for dark meson, which has previously been published through ATLAS collaboration, studied decays of dark mesons to top and bottom quarks. These top and bottom quarks subsequently decay to all jets (fully-hadronic) and (exactly) 1-lepton final states. The similarities of decay products between the dark mesons and the charged Higgs makes the dark meson search potentially sensitive to the charged Higgs signal.

    Additionally, this thesis presents a project concerning the hardware electronics of the ATLAS experiment, regarding the upgrade to the Global Trigger system for High-Luminosity Large Hadron Collider (HL-LHC). HL-LHC is the next generation LHC that will deliver much more intensive proton collisions. A software simulation program for the tau trigger was upgraded to accept full-granularity data from the calorimeter and muon systems.

    This dissertation includes previously published coauthored material.