Search for a heavy composite Majorana neutrino in events with dilepton signatures from proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This paper reports a search for heavy Majorana neutrinos in proton-proton collisions at 13 TeV, setting new limits on their mass and compositeness scale, and finding no evidence of their existence within the explored parameter space.

Contribution

It introduces a novel search for heavy Majorana neutrinos within a compositeness model using CMS data, extending the exclusion limits significantly beyond previous results.

Findings

Excluded N_e and N_mu masses below 6.0 and 6.1 TeV respectively.

Set upper limits on cross section and branching fraction as functions of mass and scale.

No significant deviation from the Standard Model observed.

Abstract

Results are presented of a search for a heavy Majorana neutrino N$_\ell$ decaying into two same-flavor leptons $\ell$ (electrons or muons) and a quark-pair jet. A model is considered in which the N$_\ell$ is an excited neutrino in a compositeness scenario. The analysis is performed using a sample of proton-proton collisions at $\sqrt{s}$ = 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$_\ell$ is produced in association with a lepton, followed by the decay of the N$_\ell$ 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$_\ell$ mass $m_{\text{N}_\ell}$ and the compositeness scale $\Lambda$. For this model the data exclude the existence of N$_\text{e}$ (N$_\mu$) for $m_{\text{N}_\ell}$ below 6.0 (6.1) TeV, at the limit where $m_{\text{N}_\ell}$ is equal to $\Lambda$. For $m_{\text{N}_\ell}$ $\approx$ 1 TeV, values of $\Lambda$ 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.