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

Open Access
Regular Article - Experimental Physics


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 → γA → γμ+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 2σ exclusion limits on the mixing parameter are ϵ ≲ 10−3-10−2. The CEPC with \( \sqrt{s}=240 \) GeV and FCC-ee with \( \sqrt{s}=160 \) 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 \( \sqrt{s}=350 \) 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 \( \sqrt{s}=240 \) 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 → γA with dark photon decay into several other channels at future e+e colliders.


Beyond Standard Model e+-e- Experiments 


Open Access

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Copyright information

© The Author(s) 2018

Authors and Affiliations

  • Min He
    • 1
  • Xiao-Gang He
    • 1
    • 2
    • 3
  • Cheng-Kai Huang
    • 2
  • Gang Li
    • 2
  1. 1.T-D. Lee Institute and School of Physics and AstronomyShanghai Jiao Tong UniversityShanghaiChina
  2. 2.Department of PhysicsNational Taiwan UniversityTaipeiR.O.C.
  3. 3.National Center for Theoretical SciencesHsinchuR.O.C.

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