Production and constraints of massive dark photon in electron-positron colliders

Dark sectors may couple to the Standard Model via one or more mediator particles. In this paper, we discuss two types of mediators: the dark photon \begin{document}$ A^{\prime} $\end{document} and the dark scalar mediator \begin{document}$ \phi $\end{document} . The total cross sections and various differential distributions of signal processes of \begin{document}$ e^{+} e^{-} \rightarrow q \bar{q} A^{\prime} $\end{document} and \begin{document}$ e^{+} e^{-} \rightarrow q \bar{q} \phi $\end{document} ( \begin{document}$ q = u,\; d,\; c,\; s $\end{document} and b quarks) are discussed, and then we focus on an invisible \begin{document}$ A^{\prime} $\end{document} study due to the cleaner background processes at future \begin{document}$ e^{+} e^{-} $\end{document} colliders. It is found that kinematic distributions of the two-jet system can be used to identify or exclude the dark photon and dark scalar mediator, as well as distinguish between them. We further study the possibility of the search for dark photon at future CEPC experiment with \begin{document}$ \sqrt{s} = 91.2 $\end{document} GeV and 240 GeV. Running at \begin{document}$ \sqrt{s} = $\end{document} 91.2 GeV, it is possible for CEPC to perform a decisive measurement on dark photon (20 GeV \begin{document}$ 60 GeV) in less than one operating year. The lower limits of integrated luminosity for significance \begin{document}$ S/\sqrt{B} = $\end{document} 2 \begin{document}$ \sigma $\end{document} , 3 \begin{document}$ \sigma $\end{document} and 5 \begin{document}$ \sigma $\end{document} are presented.