Exploration of extended Higgs sectors, development of a displaced track trigger, and improvements in GRID middleware

Sammanfattning: Two possible solutions to the Standard Model (SM) fine-tuning problem are presented in this thesis, MSSM and Compositeness. The Higgs sector of the MSSM can be tested by searching for charged Higgs bosons. Two direct searches for charged Higgs bosons decaying into a top- and bottom-quark are performed using 13.2 and 36.1 fb–¹ respectively of pp collision data collected at √s = 13 TeV with the ATLAS detector. No significant excess over the SM background is observed and upper limits on σ(pp→tbH+)×B(H+→tb) between 0.07 and 2.9 pb are set at a 95% confidence level in the charged Higgs boson mass range 200–2000 GeV using the CLs method. The phenomenology of a vector-like top-partner decaying into a BSM (pseudo-) scalar is explored and interpreted in 2HDM and Compositeness models. The experimental reach is evaluated using γγ and Zγ final states, and the LHC is determined to be sensitive to top-partner and (pseudo-) scalar masses in the 1–2 TeV range both in the Run 2 and expected Run 3 datasets. Two hardware based hit collection methods targeting long-lived particles are studied for a regional track trigger in anticipation of the HL-LHC upgrade. The efficiency is estimated to be ~20% for a wide range of track parameters for tracks originating from a displaced vertex. The prospect of using GPU-computing on the LHC GRID is considered. Extensions of the ARC middleware Information Providers integrating local GPU information are demonstrated.