Search for lepton flavour violation in top quark interactions with an up-type quark, a muon, and a tau lepton

CMS Physics Analysis Summaries
Report number	CMS-PAS-TOP-22-011
Title	Search for lepton flavour violation in top quark interactions with an up-type quark, a muon, and a tau lepton
Corporate author(s)	CMS Collaboration
Collaboration	CMS Collaboration
Subject category	Particle Physics - Experiment
Accelerator/Facility, Experiment	CERN LHC ; CMS
Abstract	We present a search for charged-lepton flavour violation (CLFV) in the top quark (t) sector using $138~\mathrm{fb}^{-1}$ of proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of $13~\mathrm{TeV}$. The analysis focuses on events containing a single muon ($\mu$) and a hadronically decaying $\tau$ lepton. Machine learning multiclass classification techniques are used to distinguish signal from standard model background events. The CLFV signal consists of the production of a single top quark via a CLFV interaction or top quark pair production followed by a CLFV decay. The results of this search are consistent with the standard model expectations. The upper limits at $95\%$ confidence level on the branching fraction $\mathcal{B}$ for CLFV top quark decays to an up (u) or a charm (c) quark, a muon and a $\tau$ lepton are $\mathcal{B}(\mathrm{t} \to \mu\tau\mathrm{u}) < 0.04$, $0.078$, and $0.118 \times 10^{-6}$, and $\mathcal{B}(\mathrm{t} \to \mu\tau\mathrm{c}) < 0.81$, $1.71$, and $2.05 \times 10^{-6}$ for scalar, vector, and tensor-like operators, respectively.
Email contact: [email protected] Fulltext in PDF Figure_003-a Figure_003-c Figure_003-b Figure_004-a Figure_002-d Figure_004-b Figure_002-a Figure_002-b Figure_002-c Figure_005-b Figure_005-a Figure_001-c Figure_001-b Figure_001-a Additional information for the analysis (restricted access)