Production and constraints for a massive dark photon at electron-positron colliders * * This work was supported in part by the National Natural Science Foundation of China (11875179, 11325525, 11635009, 11775130, 11905112), the Natural Science Foundation of Shandong Province (ZR2017MA002, ZR2019QA012) and the Fundamental Research Funds of Shandong University (2019GN038)

Abstract

Dark sector may couple to the Standard Model via one or more mediator particles. We discuss two types of mediators: the dark photon and the dark scalar mediator . The total cross-sections and various differential distributions of the processes and ( and b quarks) are discussed. We focus on the study of the invisible due to the cleaner background at future 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 GeV and 240 GeV. With CEPC running at 91.2 GeV, it would be possible to perform a decisive measurement of the dark photon (20 GeV 60 GeV) in less than one operating year. The lower limits of the integrated luminosity for the significance 2 , 3 and 5 are presented.