Search for magnetic monopoles in 8 TeV centre-of-mass energy proton-proton collisions with the ATLAS detector at the LHC

Symmetry is fundamental to our understanding of the laws of nature. The simplicity that is found in the symmetries that explain the most fundamental interactions is remarkably beautiful. Physicists have worked hard and continue to work even harder to deepen the understanding of nature with the hope of revealing higher symmetries, among them the symmetry between electricity and magnetism, but one piece is still missing from this puzzle: the elusive magnetic monopole. This dissertation presents a search for magnetic monopoles produced at the Large Hadron Collider in 8 TeV centre-of-mass energy proton–proton collisions using the ATLAS detector. The highly ionizing nature of monopoles was exploited to look for regions of high ionization density in the Transition Radiation Tracker and energy deposits in the Liquid-Argon electromagnetic calorimeter with very low lateral dispersion. The search used 7 fb$^{−1}$ of data collected by a dedicated trigger for highly ionizing particles, which made the ATLAS detector sensitive to monopoles with charge greater than the Dirac charge, in particular, twice the Dirac charge, for the first time. The results of the search were interpreted for models of pair production of spin-0 and spin-1/2 monopoles through the Drell-Yan process. A model-independent interpretation of the search is also presented. In the absence of an observation of events that were consistent with the expected monopole signal, upper limits on production cross section were set for all the scenarios considered. A model-independent limit of 0.5 fb was set for monopoles in fiducial regions of high selection efficiency. Lower mass limits were obtained for pair-produced spin-0 and spin-1/2 monopoles. This search excluded pair-produced spin-1/2 monopoles with the Dirac charge with mass below 1340 GeV, the most stringent mass limit to date.