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

Abstract

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 Nl is an excited neutrino in a compositeness scenario. The analysis is performed using a sample of proton-proton collisions at √s=13 TeV recorded by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 138fb−¹. The data are found to be in agreement with the standard model prediction. For the process in which the N is produced in association with a lepton, followed by the decay of the Nl 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 mNl and the compositeness scale ∧. For this model the data exclude the existence of Ne (Nμ) for mNl below 6.0 (6.1) TeV, at the limit where mNl is equal to ∧. For mNl ≈1 TeV, values of ∧ less than 20 (23) TeV are excluded. These results represent a considerable improvement in sensitivity, covering a larger parameter space than previous searches in pp collisions at 13TeV.