Abstract: A search is performed for a heavy Majorana neutrino (N), produced in leptonic decay of a W boson propagator and decaying into a W boson and a lepton, with the CMS detector at the LHC. The signature used in this search consists of two same-sign leptons, in any flavor combination of electrons and muons, and at least one jet. The data were collected during 2016 in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb?1. The results are found to be consistent with the expected standard model background. Upper limits are set in the mass range between 20 and 1600 GeV in the context of a Type-I seesaw mechanism, on |VeN|2, |V?N|2, and |VeNV ?N * |2/(|VeN|2?+?|V?N|2), where V?N is the matrix element describing the mixing of N with the standard model neutrino of flavor ? = e, ?. For N masses between 20 and 1600 GeV, the upper limits on |V?N|2 range between 2.3 × 10?5 and unity. These are the most restrictive direct limits for heavy Majorana neutrino masses above 430 GeV.
