Search for heavy Majorana neutrinos in same-sign dilepton channels in proton-proton collisions at $\sqrt{s} =$ 13 TeV

TL;DR

This paper reports a search for heavy Majorana neutrinos in same-sign dilepton channels at 13 TeV proton-proton collisions, setting new limits on their mixing parameters and mass range, with results consistent with the standard model.

Contribution

The study provides the most restrictive direct limits for heavy Majorana neutrino masses above 430 GeV using CMS data at 13 TeV.

Findings

No significant excess over standard model backgrounds.

Upper limits on mixing parameters range from 2.3×10⁻⁵ to 1.

Mass range explored: 20 to 1600 GeV.

Abstract

A search is performed for a heavy Majorana neutrino (N), produced by leptonic decay of a W boson propagator and decaying into a W boson and a lepton, with the CMS detector at the LHC. The signature used in this search consists of two same-sign leptons, in any flavor combination of electrons and muons, and at least one jet. The data were collected during 2016 in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$. The results are found to be consistent with the expected standard model backgrounds. Upper limits are set in the mass range between 20 and 1600 GeV in the context of a Type-I seesaw mechanism, on |$V_\mathrm{eN}$|$^2$, |$V_{\mu\mathrm{N}}$|$^2$, and |$V_{\mathrm{eN}}$$V^*_{\mu\mathrm{N}}$|$^2$ / (|$V_\mathrm{eN}$|$^2$ + |$V_{\mu\mathrm{N}}$|$^2$), where $V_{\ell\mathrm{N}}$ is the matrix element describing the mixing of N with the standard model neutrino of flavor $\ell =$ e, $\mu$. For N masses between 20 and 1600 GeV, the upper limits on |$V_{\ell\mathrm{N}}$|$^2$ range between 2.3 $\times$ 10$^{-5}$ and unity. These are the most restrictive direct limits for heavy Majorana neutrino masses above 430 GeV.