In this paper we study the present and future sensitivities of the rare meson
decay facilities KOTO, LHCb and Belle II to a light dark sector of the minimal
dark abelian gauge symmetry where a dark Higgs S and a dark photon ZD​ have
masses ≲10 GeV. We have explored the interesting scenario where S
can only decay to a pair of ZD​'s and so contribute to visible or invisible
signatures, depending on the life-time of the latter. Our computations show
that these accelerator experiments can access the dark Higgs (mass and scalar
mixing) and the dark photon (mass and kinetic mixing) parameters in a
complementary way. We have also discussed how the CMS measurement of the SM
Higgs total decay width and their limit on the Higgs invisible branching ratio
can be used to extend the experimental reach to dark photon masses up to ∼10 GeV, providing at the same time sensitivity to the gauge coupling
associated with the broken dark abelian symmetry.Comment: 33 pages, 11 figure