Search for heavy composite Majorana neutrinos produced in association with a lepton and decaying into a same-flavour lepton plus two quarks at $\sqrt{s} = 13~\mathrm{TeV}$ with the CMS detector

We present a search for physics beyond the standard model in the final state with two same-flavour leptons (electrons or muons) and two quarks. The results of the measurement are interpreted in the framework of a recently proposed model, in which a heavy Majorana neutrino stems from a composite scenario. The analysis is performed using proton-proton collisions at $\sqrt{s} = 13~\mathrm{TeV}$ recorded by the CMS experiment at the CERN LHC. The data correspond to an integrated luminosity of $2.3~\mathrm{fb}^{-1}$ collected in 2015. The observed data are in good agreement with the standard model prediction. An upper limit at $95\%$ CL on the product of the cross section of the heavy composite Majorana neutrino, $N$, produced in association with a lepton times branching fraction of $N$ into a same-flavour lepton and a quark pair is calculated as a function of its mass. In this model, the presence of the heavy composite Majorana neutrinos is excluded for masses up to $4.35~\mathrm{TeV}$ and $4.50~\mathrm{TeV}$ for a value of $\Lambda$ of $5~\mathrm{TeV}$, having analysed the $\mathrm{ee qq}$ channel and the $\mu\mu\mathrm{qq}$ channel, respectively.