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Description
A search for a top-philic $Z'$ boson in the final state with an electron or a muon and jets is presented. The top-philic $Z'$ boson is produced in association with a top quark and also decays to a top quark-antiquark pair, as it couplies exclusively to top quarks. The analysis aims to identify a heavy $Z'$ boson that produces boosted top quarks, whose hadronic decay products are merged into large-radius jets. A machine learning algorithm (ParticleNet) is employed to identify such jets. The distribution of the invariant mass of the two most energetic top quark candidates is used in the search for a $Z'$ boson in the mass range of 0.5 to 3 TeV, with decay 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 the 95\% confidence level are set for the production cross section of the $Z'$ boson, for each of the decay widths as a function of its mass. % on the two-dimensional plane of decay width and $Z'$ boson mass. These results represent the most stringent constraints to date on the existence of the top-philic $Z'$ boson. The data were recorded by the CMS experiment at the CERN LHC in proton-proton collisions at $\sqrt{s} = 13$ TeV and correspond to an integrated luminosity of 138 fb$^{-1}$.
