Type: Article
Publication Date: 2013-07-23
Citations: 34
DOI: https://doi.org/10.1103/physrevd.88.012004
A search for new particles that decay into top quark pairs ($t\overline{t}$) is performed with the ATLAS experiment at the LHC using an integrated luminosity of $4.7\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of proton--proton ($pp$) collision data collected at a center-of-mass energy $\sqrt{s}=7\text{ }\text{ }\mathrm{TeV}$. In the $t\overline{t}\ensuremath{\rightarrow}WbWb$ decay, the lepton plus jets final state is used, where one $W$ boson decays leptonically and the other hadronically. The $t\overline{t}$ system is reconstructed using both small-radius and large-radius jets, the latter being supplemented by a jet substructure analysis. A search for local excesses in the number of data events compared to the Standard Model expectation in the $t\overline{t}$ invariant mass spectrum is performed. No evidence for a $t\overline{t}$ resonance is found and 95% credibility-level limits on the production rate are determined for massive states predicted in two benchmark models. The upper limits on the cross section times branching ratio of a narrow ${Z}^{\ensuremath{'}}$ resonance range from 5.1 pb for a boson mass of 0.5 TeV to 0.03 pb for a mass of 3 TeV. A narrow leptophobic topcolor ${Z}^{\ensuremath{'}}$ resonance with a mass below 1.74 TeV is excluded. Limits are also derived for a broad color-octet resonance with $\ensuremath{\Gamma}/m=15.3%$. A Kaluza--Klein excitation of the gluon in a Randall--Sundrum model is excluded for masses below 2.07 TeV.