Search for Z' bosons decaying to pairs of heavy Majorana neutrinos in proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This paper reports a search for Z' bosons decaying into pairs of heavy Majorana neutrinos using CMS data at 13 TeV, setting new limits on their masses and couplings with no significant signal observed.

Contribution

It provides the most restrictive experimental limits to date on Z' and heavy neutrino masses within a left-right symmetric model framework.

Findings

No significant excess observed beyond background expectations.

Upper limits set on Z' production cross section and branching fractions.

Exclusion of Z' masses up to 4.42 TeV in the studied model.

Abstract

A search for the production of pairs of heavy Majorana neutrinos (N$_\ell$) from the decays of Z' bosons is performed using the CMS detector at the LHC. The data were collected in proton-proton collisions at a center-of-mass energy of $\sqrt{s}$ = 13 TeV, with an integrated luminosity of 138 fb$^{-1}$. The signature for the search is an excess in the invariant mass distribution of the final-state objects, two same-flavor leptons (e or $\mu$) and at least two jets. No significant excess of events beyond the expected background is observed. Upper limits at 95% confidence level are set on the product of the Z' production cross section and its branching fraction to a pair of N$_\ell$, as functions of N$_\ell$ and Z' boson masses ($m_{\mathrm{N}_\ell}$ and $m_\mathrm{Z'}$, respectively) for $m_\mathrm{Z'}$ from 0.4 to 4.6 TeV and $m_{\mathrm{N}_\ell}$ from 0.1 TeV to $m_\mathrm{Z'}$/2. In the theoretical framework of a left-right symmetric model, exclusion bounds in the $m_{\mathrm{N}_\ell}-m_\mathrm{Z'}$ plane are presented in both the electron and muon channels. The observed upper limit on $m_\mathrm{Z'}$ reaches up to 4.42 TeV. These are the most restrictive limits to date on the mass of N$_\ell$ as a function of the Z' boson mass.