Monte Carlo Studies of the ATLAS Forward Calorimeter and of the Supersymmetric Top Quark

The Large Hadron Collider will collide 7 TeV proton beams with the intent of studying the Standard Model of Particle Physics and searching for physics be­yond. One of the general purpose detectors designed to study the high energy proton collisions is called the ATLAS detector. The Liquid Argon Forward Calorimeter (FCal) of the ATLAS detector is an important component for the studies mentioned above. The FCal contains both electromagnetic and hadronic modules and in 2003, a beam test was conducted by the ATLAS FCal group to acquire data for the energy calibration of the FCal modules. Using the H6 beam line at CERN, the beam test was performed to investigate the response of the FCal to both electrons and pions in the energy range of (10-200) GeV. In the context of this thesis work, a simulation of the beam test was incorporated into the ATLAS software framework to study the beam test data. This thesis presents results of the Geant4 simulation, which are compared to the data to quantify the performance of the FCal over the above mentioned energy range. One of the most promising extensions of the Standard Model is known as Supersymmetry and it will be a major focus of the ATLAS experiment. In super- symmetric theories, each Standard Model particle has a superpartner differing in its spin statistics. A light supersymmetric partner of the top quark (stop) is motivated by theories of electroweak baryogenesis in the Minimal Supersymmetric Standard Model (MSSM). This thesis takes a phenomenological study of an MSSM benchmark point, LST1, with a stop mass of 150 GeV, and investigates the discovery sensitivity with the ATLAS detector.