Search for heavy composite Majorana neutrinos at the High-Luminosity and the High-Energy LHC

The sensitivity of a search for heavy Majorana neutrinos with the CMS Phase-2 detector in a final state with two leptons and at least one large-radius jet is investigated. Such new particles arise in theories beyond the standard model with compositeness. The study is based on searches previously performed with Run 2 CMS data, where no evidence for a signal was found. The High-Luminosity LHC (HL-LHC) with a centre-of-mass energy of 14 TeV and an integrated luminosity of 3 ab$^{-1}$ will allow an extension of the sensitivity to cross sections of order of a few ab for heavy neutrino masses $M(N_\ell)$ ranging from 3 to 9 TeV for the $\ell \ell q\bar{q}^\prime$ channel, where $\ell$ is an electron or a muon and $q$ is a quark. For the compositeness scale $\Lambda=M(N_\ell)$, the existence of a heavy Majorana neutrino could be excluded for masses up to 8 TeV at the $95\%$ confidence level. The projection of the study to the High-Energy LHC (HE-LHC) scenario, with a centre-of-mass energy of 27 TeV, is also presented here.