A Search For New Physics Using tt(bar) Resonances in the Lepton Plus Jets Channel at √(s) = 8 TeV in 20 fb⁻¹ of pp Collision Data at the ATLAS Experiment

Abstract

Many Beyond Standard Model theories predict particles that couple strongly to top/anti-top quark pairs. This makes tt(bar) a promising signature for new physics searches. The analysis presented in this dissertation uses 20.3 fb⁻¹ of √s = 8 TeV pp collision data from the ATLAS experiment to search for evidence of new physics in the single-lepton plus jets tt(bar) decay channel. This is done by requiring one electron or muon, large missing transverse momentum and additional hadronic jets. The tt(bar) system is reconstructed using techniques optimized for either resolved or boosted event topologies. The results of the analysis are used to set upper limits on the production cross-section times branching ratio for heavy resonances decaying to tt(bar). These limits are interpreted in the context of several benchmark models including the leptophobic topcolor Z', the Randall-Sundrum Kaluza-Klein gluon (gKK), the Randall-Sundrum Kaluza-Klein graviton (GKK) and a spin-0 scalar particle.