Searching for New High Mass Resonances in the Dielectron Channel, using the ATLAS Detector at CERN

Abstract

A search is conducted in the dielectron channel for beyond the Standard Model high mass neutral resonances, such as E6 motivated Z′ states and the Randall-Sundrum Graviton. The data in this thesis was recorded by the ATLAS detector during proton-proton collisions in 2011 at √s = 7 TeV, provided by the Large Hadron Collider at CERN in Geneva, Switzerland. The dataset used constitutes a total integrated luminosity of 2.12 fb−1 after data quality checks. The dielectron channel result is presented and combined with the equivalent 1.21 fb−1 dimuon channel result for the Z′. Additionally these results are combined with the 2.12 fb−1 diphoton channel result for the RS Graviton. The greatest excess in the dielectron channel is observed at 580 GeV with a significance of 1.34 σ. Therefore as no significant excess is observed in data above the Standard Model expectation, exclu- sion limits are set at 95% confidence level on the cross section times branching ratio for various signal scenarios as a function of resonance mass. A combined lower mass limit of 1.96 TeV is set on the ZS′ SM, and 1.95 TeV for a Randall-Sundrum Graviton with k/MPl = 0.10. These limits represent the world’s highest observed mass exclusion for the models considered, at the time of writing this thesis.