Single top quark production as a probe of anomalous tqγ and tqZ couplings at the FCC-ee

Abstract In this paper, a detailed study to probe the top quark Flavour-Changing Neutral Currents (FCNC) tqγ and tqZ at the future e − e + collider FCC-ee in two different center-of-mass energies of 240 and 350 GeV is presented. A set of useful variables are proposed and used in a multivariate technique to separate signal e − e + → Z / γ → t q ¯ ( t ¯ q ) from Standard Model background processes. The study includes a fast detector simulation based on the delphes package to consider the detector effects. The upper limits on the FCNC branching ratios at 95% confidence level (CL) in terms of the integrated luminosity are presented. It is shown that with 300 fb − 1 of integrated luminosity of data, FCC-ee would be able to exclude the effective coupling strengths above O ( 10 − 4 − 10 − 5 ) which is corresponding to branching fraction of O ( 0.01 − 0.001 ) %. We show that moving to a high-luminosity regime leads to a significant improvement on the upper bounds on the top quark FCNC couplings to a photon or a Z boson.

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