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.
Highlights
Searching for dark sector particles, including dark matter (DM) itself and other associated states, is a central goal of many experimental programs around the world
We have presented a comprehensive study on exotic Z decay at future Z factories, with emphasis on its prospects for exploring dark sector models
A Z factory provides a clean environment for decay modes which can be overwhelmed by a large background at hadron colliders
Summary
Searching for dark sector particles, including dark matter (DM) itself and other associated states, is a central goal of many experimental programs around the world. Since the dark sector particles typically only have weak couplings with the Standard Model, colliders with higher luminosity are natural places to lead this quest. In addition to using exotic decay measurements to probe these models, we compare the reach with direct and indirect dark matter detection experiments, current limits from collider searches, and estimated sensitivities of the high luminosity run of the LHC (HL-LHC). Large Electron-Positron collider (LEP) has searched for exotic Z decays into light Higgs [61,62], two light Higgs in the minimal supersymmetric Standard Model [63], photon and missing energy [64,65,66], and three photons [67].
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