Search for a heavy dark photon at future e+e− colliders

• Published in: The journal of high energy physics 2018-03, Vol.2018 (3), p.1-20, Article 139
• Main Authors: He, Min, He, Xiao-Gang, Huang, Cheng-Kai, Li, Gang
• Format: Article
• Language: English
• Subjects: Beyond Standard Model; Classical and Quantum Gravitation; e+-e- Experiments; Electron-positron accelerators; Elementary Particles; High energy physics; Large Hadron Collider; Parameter sensitivity; Parameters; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Quantum Physics; Regular Article - Experimental Physics; Relativity Theory; Standard model (particle physics); String Theory; Superconducting supercolliders
• ISSN: 1029-8479; 1029-8479
• DOI: 10.1007/JHEP03(2018)139

A bstract A coupling of a dark photon A ′ from a U(1) A ′ with the standard model (SM) particles can be generated through kinetic mixing represented by a parameter ϵ . A non-zero ϵ also induces a mixing between A ′ and Z if dark photon mass m A ′ is not zero. This mixing can be large when m A ′ is close to m Z even if the parameter ϵ is small. Many efforts have been made to constrain the parameter ϵ for a low dark photon mass m A ′ compared with the Z boson mass m Z . We study the search for dark photon in e + e − → γ A ′ → γ μ + μ − for a dark photon mass m A ′ as large as kinematically allowed at future e + e − colliders. For large m A ′, care should be taken to properly treat possible large mixing between A ′ and Z . We obtain sensitivities to the parameter ϵ for a wide range of dark photon mass at planed e + e − colliders, such as Circular Electron Positron Collider (CEPC), International Linear Collider (ILC) and Future Circular Collider (FCC-ee). For the dark photon mass 20 GeV ≲ m A ′ ≲ 330 GeV, the 2 σ exclusion limits on the mixing parameter are ϵ ≲ 10 −3 -10 −2 . The CEPC with s = 240 GeV and FCC-ee with s = 160 GeV are more sensitive than the constraint from current LHCb measurement once the dark photon mass m A ′ ≳ 50 GeV. For m A ′ ≳ 220 GeV, the sensitivity at the FCC-ee with s = 350 GeV and 1 . 5 ab −1 is better than that at the 13 TeV LHC with 300 fb −1 , while the sensitivity at the CEPC with s = 240 GeV and 5ab −1 can be even better than that at 13TeV LHC with 3ab −1 for m A ′ ≳ 180 GeV. We also comment on sensitivities of e + e − → γ A ′ with dark photon decay into several other channels at future e + e − colliders.