Topics in the measurement of electrons with the ATLAS detector at the LHC

Upon completion in 2008, the Large Hadron Collider (LHC) will accelerate and collide protons with a 14~TeV center-of-mass energy at a designed luminosity of $10^{34}\rm {cm^{-2}s^{-1}}$. The LHC will also be able to accelerate and collide heavy ions (Pb-Pb) at a nucleon-nucleon center of mass of 5.5~TeV. It will be the most powerful instrument ever built to investigate particles properties. The ATLAS (A Toroidal LHC ApparatuS) experiment is one of five experiments at the LHC. ATLAS is a general-purpose detector designed for the discovery of new particles predicted by the Standard Model (i.e Higgs boson), and of signatures of physics beyond the Standard Model (i.e supersymmetry). These discoveries require a highly efficient detection and high-resolution measurement of leptons or photons in the final state. In ATLAS, the liquid Argon (LAr) calorimeters identify and measure electrons and photons with high resolution. This dissertation reports on a study of various topics relevant to the measurement of electrons and photons with the LAr calorimeters. We report on the design and construction and testing of the High Voltage Feedthroughs (HVFTs). The HVFTs carry high-voltage lines to the calorimeter cells in the liquid, while maintaining the electrical and cryogenic integrity of the system. Seven HVFTs, including one spare, designed and built at Stony Brook are installed on the ATLAS calorimeters at CERN. It is shown that the inacce ssible parts of the HVFTs are expected to operate without failures in excess of 20 years. We also report on the description and simulation of the inactive material installed in the gap between the barrel and the two end-cap cryostats of the LAr calorimeters. It is known that a detailed knowledge of the upstream material is required to properly calibrate the calorimeter energy measurement with electrons from well-known resonances. Simulations show that the amount of materials in the gap is consistent with the early estimates used in the Calorimeter Performance Technical Design Report and therefore does not impact the $e/\gamma$ energy resolution beyond what was predicted. Finally we report on results of photon runs from the 2004 Combined Test Beam (CTB) and compare this data to photon simulations done with the ATLAS software.