Luminosity determination and searches for supersymmetric sleptons and gauginos at the ATLAS experiment

This thesis documents my work in the luminosity and supersymmetry groups of the ATLAS experiment at the Large Hadron Collider. The theory of supersymmetry and the concept of luminosity are introduced. The ATLAS experiment is described with special focus on a luminosity monitor called LUCID. A data-driven luminosity calibration method is presented and evaluated using the LUCID detector. This method allows the luminosity measurement to be calibrated for arbitrary inputs. A study of particle counting using LUCID is then presented. The charge deposited by particles passing through the detector is shown to be directly proportional to the luminosity. Finally, a search for sleptons and gauginos in final states with exactly two oppositely charged leptons is presented. The search is based on 20.3 fb$^{-1}$ of $pp$ collision data recorded with the ATLAS detector in 2012 at a center-of-mass energy of $\sqrt{s} = 8$ TeV. No significant excess over the Standard Model expectation is observed. Instead, limits are set on the slepton and gaugino masses.