Lifetime of the dark Z boson

The mediator particle between the Standard Model sector and a hidden sector might have a long lifetime to show the observable displaced vertices in experiments. Considering a fermionic dark matter model in which the hidden sector is connected to the Standard Model by an additional Higgs doublet field, the mediator dark Z boson may live long enough. We explore the possibility to observe the displaced vertices of the long-lived dark Z boson at the CERN LHC and at the proposed SHiP experiment. We find that the ATLAS and CMS searches for the long-lived dark Z boson can probe the mass range 7 < m Z ′ < 150 MeV with 150 fb - 1 integrated luminosity at the LHC run 3, and the SHiP experiment will probe 2 m e < m Z ′ < 15 MeV range with 6 × 10 20 protons on target in total 15 years. The dark matter phenomenology is also discussed in the region where such a long-lived mediator is detectable.