Search for heavy composite Majorana neutrino

This note describes a search for a heavy Majorana neutrino $\mathrm{N}_{\ell}$ in the final state with two same-flavor leptons $\ell$ (electrons or muons) and two quarks. In the model considered, $\mathrm{N}_{\ell}$ arises from a composite scenario. The analysis is performed using a sample of proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$ recorded by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of $138~\mathrm{fb}^{-1}$. The observed data are in agreement with the standard model prediction. For a process in which $\mathrm{N}_{\ell}$ is produced in association with a lepton, followed by the decay of $\mathrm{N}_{\ell}$ to a same-flavor lepton and a quark pair, an upper limit at $95\%$ confidence level on the cross section times branching fraction is obtained as a function of the $\mathrm{N}_{\ell}$ mass $m_{\mathrm{N}_{\ell}}$. In this model, the data exclude $\mathrm{N}_{\mathrm{e}}$ ($\mathrm{N}_{\mu}$) for $m_{\mathrm{N}_{\ell}}$ below 5.50 (5.70) TeV in the limit where the compositeness scale $\Lambda$ is equal to $m_{\mathrm{N}_{\ell}}$, and below 5.10 (5.50) TeV with the more restrictive requirement that the unitarity bound is satisfied over the full phase space of parton motion within the proton.