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