Search for Magnetic Monopoles and Other Highly Ionizing Particles in 13 TeV Centre-of-Mass Energy Proton-Proton Collisions with the ATLAS Detector at the LHC

Among the outstanding questions of particle physics, proof of the existence of a magnetic monopole is still one of great interest. One compelling argument that motivates the search for magnetic monopoles is Paul Dirac's finding that the seemingly inexplicable quantized nature of the electric charge can be explained through the existence of magnetic monopoles. TeV-mass Dirac magnetic monopoles could potentially be produced by the sqrt{s} = 13 TeV proton-proton collisions at the LHC. This thesis documents a search for magnetic monopoles using a 138 fb^-1 dataset of Run 2 proton-proton collisions at the LHC collected by the ATLAS experiment. Due to the highly ionizing nature of the interaction of magnetic monopoles with matter, the search is extended to include other highly ionizing particles known as high electric charge objects. Two production mechanisms are considered as benchmark models to interpret the results, Drell-Yan and photon fusion. No spin constraints are imposed by Dirac's theory, and therefore both spin-0 and spin-1/2 are modelled. The collision conditions allow for masses between 0.2 and 4TeV to be studied. Theoretical considerations and experimental constraints motivate studying magnetic charges |g|= 1 and 2 g_D for magnetic monopoles and the range of |z| = 20 through |z| = 100 for high electric charge objects. Detection is based on the particle's characteristic high ionization of matter, penetration distance in the detector and lack of calorimeter shower. A data driven method is used to estimate the background contamination. No excess events are found in the signal region. Cross-section limits are computed through the CLs method with 95% confidence level. The highest mass limits to date for particle collider highly ionizing particle searches are presented.