Search for Z′ bosons decaying to pairs of heavy Majorana neutrinos in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A search for the production of pairs of heavy Majorana neutrinos (N ℓ ) from the decays of Z′ bosons is performed using the CMS detector at the LHC. The data were collected in proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV, with an integrated luminosity of 138 fb −1. The signature for the search is an excess in the invariant mass distribution of the final-state objects, two same-flavor leptons (e or μ) and at least two jets. No significant excess of events beyond the expected background is observed. Upper limits at 95% confidence level are set on the product of the Z′ production cross section and its branching fraction to a pair of N ℓ , as functions of N ℓ and Z′ boson masses ( ${m}_{{N}_{\ell }}$ and ${m}_{{Z}^{\prime }}$ , respectively) for ${m}_{{Z}^{\prime }}$ from 0.4 to 4.6 TeV and ${m}_{{N}_{\ell }}$ from 0.1 TeV to ${m}_{{Z}^{\prime }}$ /2. In the theoretical framework of a left-right symmetric model, exclusion bounds in the ${m}_{{N}_{\ell }}$ - ${m}_{{Z}^{\prime }}$ plane are presented in both the electron and muon channels. The observed upper limit on ${m}_{{Z}^{\prime }}$ reaches up to 4.42 TeV. These are the most restrictive limits to date on the mass of N ℓ as a function of the Z′ boson mass.