Tumasyan, A.Adam, W.Andrejkovic, J. W.Bergauer, T.Chatterjee, S.Damanakis, K.The ATLAS collaboration2024-03-092024-03-0920230370-26931873-2445https://doi.org/10.1016/j.physletb.2023.137803https://hdl.handle.net/20.500.14034/1328Results are presented of a search for a heavy Majorana neutrino N ? decaying into two same-flavor leptons ? (electrons or muons) and a quark-pair jet. A model is considered in which the N ? is an excited neutrino in a compositeness scenario. The analysis is performed using a sample of proton-proton collisions at & RADIC;s = 13 TeV 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 N ? is produced in association with a lepton, followed by the decay of the N ? 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 N ? mass mN ? and the compositeness scale ?. For this model the data exclude the existence of Ne (N & mu;) for mN ? below 6.0 (6.1) TeV, at the limit where mN ? is equal to ?. For mN ? N 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 13 TeV.& COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.eninfo:eu-repo/semantics/openAccessCms; Lhc; Composite Fermions; Heavy LeptonsArticle10.1016/j.physletb.2023.137803843N/AWOS:001038664500001Q1