Study of R-parity Violating Decays of Supersymmetric Particles with the ATLAS Detector at the LHC

Supersymmetry is a space-time symmetry that postulates the existence of new particles. It assigns to each Standard Model fermion (boson) an associated supersymmetric boson (fermion) partner with the same quantum numbers except for spin. The introduction of these new supersymmetric particles provides a potential solution to the hierarchy problem. Discovery of such particles or alternatively an exclusion of a certain supersymmetic parameter space is one of the main purposes of collider experiments. A special scenario of Supersymmetry that enables the decay of the lightest supersymmetric particle to Standard Model particles is studied using proton-proton collision data collected by the ATLAS experiment at center-of-mass energy of 13 TeV. The searched signal is characterized by a final state of at least four leptons, which leads to extraordinarily low background contributions from Standard Model processes. The work described in this thesis assisted to an exclusion of the considered supersymmetric model for hypothesized mass of the lightest supersymmetric particle of up to 1.1 TeV. Although the size of background contributions is small in this analysis, it has to be measured as precisely as possible in order to set most stringent limits on higher lightest supersymmetric particle mass regimes. This thesis concentrates on a special type of Standard Model background that does not arise in primary interaction processes but is a result of wrongly identified or secondarily emerging leptons that contribute to the four-lepton final state. A data-driven method is presented to estimate this kind of background.