Exposing Dark Sector with Future Z-Factories

Abstract

We investigate the prospects of searching dark sector models via exotic Z-boson decay at future $e^{+}{e}^{-}$ colliders with Giga Z and Tera Z options. Four general categories of dark sector models: Higgs portal dark matter, vector portal dark matter, inelastic dark matter and axion-like particles, are considered. Focusing on channels motivated by the dark sector models, we carry out a model independent study of the sensitivities of Z-factories in probing exotic decays. The limits on branching ratios of the exotic Z decay are typically $\mathcal{O}(10^{-6}-10^{-8.5})$ for the Giga Z and $\mathcal{O}(10^{-7.5}-10^{-11})$ for the Tera Z, and they are compared with the projection for the high luminosity LHC. We demonstrate that future Z-factories can provide its unique and leading sensitivity, and highlight the complementarity with other experiments, including the indirect and direct dark matter search limits, and the existing collider limits. Future Z factories will play a leading role to uncover the hidden sector of the universe in the future.

Comments: 42 pages, 16 figures, 2 tables. v2: references added, particle separation improved, minor changes in figures, version matched to the journal