Search for Resonances Decaying into Top Quark Pairs Using Fully Hadronic Decays in pp Collisions with ATLAS at sqrt(s) = 7 TeV

A search for heavy resonances decaying into top quark pairs is presented. Proton-proton collison events recorded with the ATLAS detector at the Large Hadron Collider running at a centre-of-mass energy of 7 TeV corresponding to an integrated luminosity of $4.7$ fb$^{-1}$ are used. The $t\bar{t}$ events are reconstructed by selecting two top quarks in their fully hadronic decay modes which are reconstructed using the Cambridge/Aachen jet finder algorithm with a radius parameter of $1.5$. The substructure of the jets is analysed using the HEPTopTagger algorithm to separate top quark jets from those originating from gluons and lighter quark jets. The jets are also required to be associated with a $b$-tagged jet of smaller radius. The invariant mass spectrum of the data is compared to the Standard Model prediction, and no evidence for resonant production of top quark pairs is found. The data are used to set upper limits on the cross section times branching ratio for resonant $t\bar{t}$ production in two models at 95% confidence level. Leptophobic Z' bosons with masses between 700 and 1300 GeV and Kaluza-Klein-Gluons with masses between 700 and 1500 GeV are excluded at the 95% confidence level.