Search for Z′ bosons decaying to pairs of heavy Majorana neutrinos in proton-proton collisions at √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 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 (mN_ℓ and mZ_′, respectively) for mZ_′ from 0.4 to 4.6 TeV and mN_ℓ from 0.1 TeV to mZ_′/2. In the theoretical framework of a left-right symmetric model, exclusion bounds in the mN_ℓ-mZ_′ plane are presented in both the electron and muon channels. The observed upper limit on mZ_′ 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.