Dark Photon Searches Using Displaced Vertices at Low Energy 𝑒⁺𝑒⁻ Colliders

Figure 4

Explorable region for cases (a) solid, (b) dashed, and (c) dotted in the plane 𝜖-𝑚_𝛾′. No instrumental backgrounds are taken into consideration, as well as potential efficiency and resolution effects for the detector. Above ~210 MeV, the opening of the 2-muon channel drastically reduces the effectiveness of the method.