Supersymmetry or Universal Extra Dimensions? Utilizing the ATLAS Experiment at CERN

Supersymmetry and Universal Extra Dimensions are just two of an array of popular and enticing extensions to the Standard Model. The work presented in this thesis evaluates the feasibility of differentiating between these two models by measuring the spins of the new particles, utilising the ATLAS experiment at the Large Hadron Collider at CERN. The method presented depends upon the use of an angular variable, cos θ∗ ll, which is sensitive to the polar angle in the direct slepton pair production process: qq → Z0/γ∗ → ˜l± ˜l∓ → χ˜0 1l ±χ˜0 1l ∓. This angular variable is advantageous since it is longitudinally boost invariant along the beam axis. This allows it to be used at the Large Hadron Collider where the initial centre-of-mass frame of reference is unknown and unrecoverable owing to the presence of invisible particles in the event. The work invoked Monte Carlo events, fully simulated in accordance with the mSUGRA Supersymmetry model corresponding to a selected production point in mSUGRA space of the ATLAS detector. It was demonstrated that, using this method and given the Monte Carlo simulation at this test point, the Large Hadron Collider can distinguish between the supersymmetric production angular distribution and that of UED using 30 fb−1 of integrated luminosity. A further part of the work involved an investigation into part of the innermost detector system of ATLAS. The work investigated the operational performance of a certain fraction of semiconductor tracker barrel modules utilizing data acquired during cosmic commissioning tests carried out at CERN in 2006. This included measuring the noise occupancy levels and subsequently identifying any problematic modules in the process. Eight problematic modules were identified, forming three distinct classes, each class pointing toward a different type of problem. Furthermore, an anomaly, the socalled zeroth time bin anomaly, was found and prompted further investigation to its root cause.