Searches for Supersymmetry in Multi-lepton Final States with the ATLAS Detector and Related Challenges

The ATLAS experiment at the Large Hadron Collider (LHC) is designed to address the open questions relating to high energy particle physics. Challenging experimental conditions require a worldwide distributed computing environment which allows the sharing of the work load and provides all collaboration member access to data and computing resources. NorduGrid is one of the three Grid flavors used by physicists for the LHC experiments. This thesis will describe the implementation of the ATLAS computing model in the NorduGrid environment. This computing infrastructure is an essential tool used for facilitating physics analysis. One of the main goals of the ATLAS physics program is to search for Supersymmetric extensions of the Standard Model. In many cases such models predict final states with three or more leptons. This thesis investigates the potential of the ATLAS detector to discover Supersymmetry in trilepton final states. The analysis follows a jet inclusive and exclusive path aimed at two different types of trilepton events. The area of lepton isolation has been studied in more detail leading to some suggestions for optimization of the isolation requirements. Analysis strategies developed for the constrained SUSY model with gravity mediated symmetry breaking, mSUGRA, are applied on a novel set of points generated within the MSSM24 model. The first collision data collected in December 2009 and corresponding Monte Carlo simu lation has been compared in order to obtain a preliminary impression of the understanding of the detector. Outreach activities carried out during the PhD project are also reported in the thesis.