CERN Accelerating science

CMS Physics Analysis Summaries
Report number	CMS-PAS-B2G-24-023
Title	Search for heavy neutral leptons in top quark decays with same-sign dilepton final states in proton-proton collisions at $\sqrt{s}=13~\mathrm{TeV}$
Corporate author(s)	CMS Collaboration
Collaboration	CMS Collaboration
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; CMS
Abstract	The first search for a Majorana$\text{-}$type heavy neutral lepton (N) produced in top quark decays with the CMS detector is reported. In type$\text{-}$I seesaw models, where the N mixes with the first two generations of neutrinos, these heavy leptons lead to novel top quark decay modes that violate lepton number conservation. We therefore search for top quark pair production in proton$\text{-}$proton collisions, followed by a top quark decay to a bottom quark and a W boson, decaying further into a charged lepton (electron or muon), and N. Here, the Majorana N decays to a W boson and a charged lepton with the same sign as the charged lepton produced with N. The experimental signature of this process is characterized by the presence of same$\text{-}$sign and same$\text{-}$flavor lepton pairs and jets. We use proton$\text{-}$proton collision data corresponding to an integrated luminosity of 138 $\text{fb}^{-1}$ at a center$\text{-}$of$\text{-}$mass energy of 13 TeV, collected during 2016--2018 with the CMS detector at the LHC. The search is performed for N masses between 20 and 100 GeV. Depending on the mass of N, the observed (expected) upper limits at the 95\% CL on the branching ratio of the top quark decay to N, charged lepton, and bottom quark vary between $1.1\times10^{-5}$ ($6.8\times10^{-6}$) and $4.7\times10^{-5}$ ($3.0 \times 10^{-5}$) in the dielectron final state and between $3.8\times10^{-6}$ ($3.4 \times 10^{-6}$) and $2.4\times10^{-5}$ ($1.3 \times 10^{-5}$) in the dimuon final state.
Email contact: cms-pag-conveners-b2g@cern.ch  Fulltext in PDF  Figure_013-a  Figure_013-b  Figure_012-b  Figure_010-e  Figure_010-d  Figure_012-a  Figure_010-f  Figure_010-a  Figure_010-c  Figure_010-b  Figure_009-b  Figure_009-a  Figure_011-a  Figure_011-b  Figure_011-c  Figure_011-d  Figure_007-b  Figure_003-a  Figure_003-c  Figure_003-b  Figure_003-d  Figure_008  Figure_004-d  Figure_004-b  Figure_004-c  Figure_004-a  Figure_005-c  Figure_005-b  Figure_005-a  Figure_007-a  Figure_005-d  Figure_002-d  Figure_006-a  Figure_006-b  Figure_006-c  Figure_006-d  Figure_002-a  Figure_002-b  Figure_002-c  Figure_001-d  Figure_001-c  Figure_001-b  Figure_001-a  Additional information for the analysis (restricted access)