Search for Boosted Top-Antitop Quark Resonances in Muon+Jets Events at 13 TeV Proton-Proton Collisions

A search for new heavy resonances decaying into top-antitop quark pairs is performed using proton-proton collisions at a center of mass energy of 13 TeV. The datasets correspond to an integrated luminosity of 35.9 fb−1 and were recorded by the Compact Muon Solenoid detector at The European Organization for Nuclear Research, CERN. The invariant mass spectrum of the boosted top-antitop quark system is the observable employed to probe the existence of such resonances. The analysis is optimized for events where the top quarks have a large Lorentz-boost resulting in non-isolated leptons and collimated jets from the semileptonic decay of the top quark pairs. In particular, only events where the lepton is a muon are considered. The optimization relies mostly in the application of machine learning algorithms and substructure variables that balance background reduction and signal acceptance. The results show that the Standard Model background predictions are in agreement with the observed data. Thus, a Bayesian Statitical Model is applied to set 95% Confidence Level upper limits on the production cross section times branching ratio of the selected two benchmark models; the Randall- Sundrum model that predicts Kaluza-Klein excitation of gluons, and the extended gauge model that predicts the existence of a leptophobic Topcolor Z′.