Production and constraints for a massive dark photon at electron-positron colliders

Abstract

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

17 pages, 10 figures, to be published in Chinese Physics C

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