Probing FCNC couplings in single top quark production associated with a neutral gauge boson at future lepton colliders

TL;DR

This study investigates the potential of future electron-positron colliders to detect flavor-changing neutral current interactions in single top quark production, setting upper limits on anomalous couplings using SMEFT and simulation techniques.

Contribution

It introduces a novel analysis framework for probing FCNC couplings in single top production at future colliders using SMEFT and detailed simulations.

Findings

Future colliders can probe FCNC branching fractions below 10^{-4}.

Upper limits on FCNC couplings are established at 95% confidence level.

The analysis demonstrates the sensitivity of upcoming colliders to rare top quark processes.

Abstract

In this paper, we consider a single top quark production in association with a neutral gauge boson (Z boson or Photon) at the future electron-positron colliders. We utilize these channels to probe the top quark Flavour Changing Neutral Currents (FCNC) interactions in $tqZ$ and $tq\gamma$ vertices. We perform two separate analyses for top-Z-jet and top-$\gamma$-jet channels. The Standard Model Effective Field Theory (SMEFT) approach is employed to search for these anomalous couplings. We consider parton showering, hadronization and fast detector simulation in our study and use a cut-and-count technique to separate the signal from the Standard Model (SM) background processes. The upper limits on the FCNC couplings at $95\%$ confidence level for the different integrated luminosities are obtained. It is shown that the future lepton collider would be able to probe the FCNC branching fractions to $\rm{Br}(t\rightarrow q \gamma)< 10^{-4}$ and $\rm{Br}(t\rightarrow q Z) < 10^{-4}$ with $3$ $\rm{ab}^{-1}$of integrated luminosity of data at a center of mass energy of $350$ GeV.