A search for tt resonances in lepton plus jets events with ATLAS using 14/fb of proton-proton collisions at sqrt(s) = 8 TeV
https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-CONF-2013-052/
A search for new particles that decay into top quark pairs ( ) is performed with the ATLAS experiment at the LHC using an integrated luminosity of 14 fb of proton-proton collision data collected at center-of-mass energy TeV. The lepton plus jets final state is used, where the top-pair decays as with one boson decaying leptonically and the other hadronically. The system is reconstructed using both a conventional resolved jet analysis and a large-radius jet substructure analysis. The invariant mass spectrum is searched for local excesses deviating from the Standard Model prediction. No evidence for a resonance is found and 95% CL limits on the production rate are determined for massive states in two benchmark models. The upper limits on the cross section times branching ratio of a narrow boson decaying to top pairs range from 5.3 pb for a resonance mass of 0.5 TeV to 0.08 pb for a mass of 3 TeV. A narrow leptophobic topcolor boson with a mass below 1.8 TeV is excluded. Upper limits are set on the cross section times branching ratio for a broad color-octet resonance with 15.3% decaying to . These range from 9.6 pb for a mass of 0.5 TeV to 0.152 pb for a mass of 2.5 TeV. A Kaluza-Klein excitation of the gluon in a Randall-Sundrum model is excluded for masses below 2.0 TeV.