Search for a heavy composite Majorana neutrino in events with dilepton signatures from proton-proton collisions at s=13 TeV

Results are presented of a search for a heavy Majorana neutrino Nℓ decaying into two same-flavor leptons ℓ (electrons or muons) and a quark-pair jet. A model is considered in which the Image 1 is an excited neutrino in a compositeness scenario. The analysis is performed using a sample of proton-proton collisions at roots=13TeV recorded by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 138 fb^-1. The data are found to be in agreement with the standard model prediction. For the process in which the Image 1 is produced in association with a lepton, followed by the decay of the Image 1 to a same-flavor lepton and a quark pair, an upper limit at 95% confidence level on the product of the cross section and branching fraction is obtained as a function of the Nℓ mass m Nℓ and the compositeness scale Λ. For this model the data exclude the existence of Ne(N) for for m Nℓ below 6.0 (6.1) TeV, at the limit where m Nℓ is equal to Λ. For m Nℓ=1TeV, values of Λ less than 20 (23) TeV are excluded. These results represent a considerable improvement in sensitivity, covering a larger parameter space than previous searches in Image 6 collisions at 13 TeV.