A Search for tt ̄ Resonances in the Lepton Plus Jets Channel from Proton-Proton Collisions at √s = 8 TeV with the ATLAS Detector

Abstract

A search for the resonant production of top quark pairs inproton-proton collisions at a center-of-mass energy of 8~TeV ispresented.The Large Hadron Collider delivered 14 inverse femtobarns of collisiondata which were collected by the ATLAS detector.The lepton plus jets final state is used, and the top pair invariantmass spectrum is probed for local excesses above the Standard Modelbackground prediction.No evidence for resonant top pair production is found.95\% credibility limits are set on the cross section times branchingratio of two signal benchmarks.A narrow leptophobic topcolor $Z^\prime$ boson decaying to top quarkpairs and the Kaluza-Klein excitation of the gluon in aRandall-Sundrum model are excluded for masses below 1.8 and 2.0~TeV,respectively.The expected sensitivity to new physics at ATLAS with proton-protoncollisions delivered by a High Luminosity Large Hadron Collider isalso presented.The feasibility of analyses studying vector boson scattering, exoticresonances, and an extended Higgs sector with up to 3000 inversefemtobarns of integrated luminosity is investigated based on the fastsimulation of proton-proton collisions at a center-of-mass energy of14~TeV.