Search for top quark Flavor-Changing Neutral Currents (FCNC) in multilepton final states using an effective field theory approach in proton-proton collisions at sqrt(s) = 13 TeV

CMS Physics Analysis Summaries
Report number	CMS-PAS-TOP-25-015
Title	Search for top quark Flavor-Changing Neutral Currents (FCNC) in multilepton final states using an effective field theory approach in proton-proton collisions at sqrt(s) = 13 TeV
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 flavour-changing neutral current (FCNC) interactions involving the top quark in production and decay. This analysis establishes the first global search in the top-quark FCNC sector within the standard model effective field theory where all relevant operators are constrained simultaneously in a single fit to data, providing a framework for future measurements and combinations at the LHC. The analysis uses proton--proton collision data at $\sqrt{s}=13~\mathrm{TeV}$, corresponding to an integrated luminosity of $138~\mathrm{fb}^{-1}$. Signal contributions are probed in final states with two same-sign leptons or three leptons. Multivariate discriminants are used to separate signal from background, and their distributions enter a likelihood fit to determine $95\%$ confidence intervals for 24 Wilson coefficients. No evidence for FCNC interactions is observed. The results provide the first simultaneous constraints on the complete operator set and set the most stringent limits to date on FCNC top-quark decay branching fractions via two-lepton-two-quark interactions, $\mathrm{BR}(\mathrm{t}\to \ell^{+}\ell^{-}\mathrm{q})$, where $\mathrm{q}=\mathrm{u}$ or $\mathrm{c}$.
Other source	Inspire
Email contact: cms-pag-conveners-top@cern.ch Fulltext in PDF Figure_003 Figure_001 Figure_002 Additional information for the analysis (restricted access)