Search for a top-philic Z' boson decaying into a $\mathrm{t\bar{t}}$ pair in a final state with jets and an electron or muon in proton-proton collisions at $\sqrt{s}$ = 13.6 TeV

A search for a top-philic Z' boson in a final state with jets and an electron or muon is presented. The search is based on a sample of proton-proton collision data collected at $\sqrt{s}$ = 13 TeV by the CMS experiment at the CERN LHC during 2016$-$2018, corresponding to an integrated luminosity of 138 fb$^{-1}$. The top-philic Z' boson is produced in association with a top-antitop quark pair ($\mathrm{t\bar{t}}$) and decays into a $\mathrm{t\bar{t}}$ pair, as it couples exclusively to top quarks. The analysis aims to identify a heavy Z' boson that produces Lorentz-boosted top quarks, whose hadronic decay products are merged into large-radius jets. A machine-learning algorithm is employed to identify such jets. The distribution of the invariant mass of the two top quark candidates with the highest transverse momentum is used as the discriminant variable in a Z' boson mass range of 0.5$-$3 TeV, with intrinsic widths of 4, 10, 20, and 50% relative to its mass. The results obtained are found to be in agreement with the standard model background prediction. Upper limits at 95% confidence level are set on the production cross section of the Z' boson, for each of the decay widths as a function of its mass. These results represent the most stringent constraints to date on the existence of a top-philic Z' boson.