Search for resonant $\mathrm{t\bar{t}}$ production in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$

A search for a heavy resonance decaying into top quark and antiquark $(\mathrm{t\bar{t}})$ pairs is performed using proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$. The search uses the full data set collected with the CMS detector in 2016, which corresponds to an integrated luminosity of $36~\mathrm{fb}^{-1}$. The analysis is split into three exclusive final states and uses reconstruction techniques that are optimized for top quarks with high Lorentz boosts, which requires the use of nonisolated leptons and jet substructure techniques. No significant excess of events relative to the expected yield from standard model processes is observed. Upper limits on the production cross section of heavy resonances decaying to $\mathrm{t\bar{t}}$ are calculated. Limits are derived for a leptophobic topcolor $\mathrm{Z}^{\prime}$ resonance with widths of $1\%$, $10\%$, and $30\%$ relative to the mass of the resonance. Additional exclusion limits are set for a Kaluza--Klein (KK) excitation of the gluon in the Randall--Sundrum model and a model where a narrow $\mathrm{Z}^{\prime}$ resonance is exclusively produced in association with jets. To date, these are the most stringent limits on a $\mathrm{t\bar{t}}$ resonance.