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

TL;DR

This paper explores the production of dark photons and scalars at electron-positron colliders, analyzing their signatures, and assesses the potential for future experiments like CEPC to detect or exclude these particles.

Contribution

It introduces a detailed analysis of dark photon and scalar mediator production at e+e- colliders, focusing on invisible dark photon detection and kinematic discrimination methods.

Findings

Kinematic distributions can distinguish dark photon from scalar mediators.

CEPC can decisively measure dark photons with masses between 20 and 60 GeV.

Lower luminosity thresholds for discovery are provided for future collider runs.

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 $\phi$. The total cross-sections and various differential distributions of the processes $e^{+} e^{-} \rightarrow q \bar{q} A^{\prime}$ and $e^{+} e^{-} \rightarrow q \bar{q} \phi$ ($q=u,~d,~c,~s$ 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.