Top-Charm Associated Production in High Energy e + e − Collisions ∗

The possibility of exploring the flavor changing neutral current $tcZ/tc\ensuremath{\gamma}$ couplings in the production vertex for the reaction ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}t\overline{c}+\overline{t}c$ is examined. Using a model independent parametrization for the effective Lagrangian to describe the most general three-point interactions, production cross sections are found to be relatively small at CERN LEP II, but potentially sizable at higher energy ${e}^{+}{e}^{\ensuremath{-}}$ colliders. The kinematic characteristics of the signal are studied and a set of cuts are devised for clean separation of the signal from background. The resulting sensitivity to anomalous flavor changing coupling at LEP II with an integrated luminosity of $4\ifmmode\times\else\texttimes\fi{}500{\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ is found to be comparable to their present indirect constraints from loop processes, while at higher energy colliders with 0.5\char21{}1 TeV center-of-mass energy and 50\char21{}200 ${\mathrm{fb}}^{\mathrm{\ensuremath{-}}1}$ luminosity, one expects to reach a sensitivity at or below the percentage level.