A Search for $t\bar{t}$ Resonances in the Lepton Plus Jets Channel using 2.05 fb$^{-1}$ of $pp$ Collisions at $\sqrt{s} = 7$ TeV

A search for top quark pair ($t\bar{t}$) resonances in the lepton plus jets final states has been performed with the ATLAS experiment at the LHC. The search uses a data sample corresponding to an integrated luminosity of 2.05 fb$^{-1}$, and was recorded in 2011 at a proton-proton centre-of-mass energy of 7 TeV. Limits are set on the production cross-section times branching ratio to top quark pairs of such resonances, ranging from approximately 9.3 pb at $m=$ 500~GeV to 0.95 pb at $m=$ 1300~GeV, excluding a leptophobic topcolour $Z'$ boson with 500~GeV $< m_{\rm Z'} <$ 860 GeV at 95\% probability. In Randall-Sundrum models, Kaluza-Klein gluons with masses between 500 and 1025 GeV are excluded at 95\% probability.