摘要
We investigate the discovery potential of multi-TeV muon colliders for a heavy dark Z boson (ZD) with a mass above 1 TeV, via the associated production process mu+mu- -* ZD gamma. This process enables precise reconstruction of MZD through the photon recoil mass (mrecoil). Focusing on the ZD -* jjX and ZD -* e+e- decay modes, we present strategies to achieve high sensitivity to the kinetic mixing parameter epsilon at 3, 6, and 10 TeV muon colliders with integrated luminosities of 1, 4, and 10 ab-1, respectively, assuming that ZD decays exclusively into Standard Model particles. We apply mass-dependent cuts on mrecoil and mee to account for the energy-dependent detector response. For heavier MZD, the associated photon becomes less energetic, leading to better photon energy resolution and enabling more stringent mrecoil cuts. Conversely, for lighter MZD, the lower-energy electron pair from ZD -* e+e- allows tighter invariant mass (mee) cuts. By combining these complementary mrecoil- and mee-based selections across both the jjX and e+e- channels, we achieve sensitivity to epsilon down to O(10-3) as MZD approaches pffiffis, substantially surpassing the projected reach of a 100 TeV proton-proton collider. Even if ZD decays into dark-sector particles, the recoil mass method remains effective, highlighting muon colliders as powerful facilities for exploring heavy dark sectors.