NCTS Activity - Particle Physics Journal Club 2018/3/26 (Mon.) 12:30

[Chao-Jung Kuo]

*** NCTS Activity  ***

Particle Physics Journal Club

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Speaker : Dr. Gang Li (NTU)

Title :  Search for a heavy dark photon at future e^+e^- colliders 

Time : 2018/3/26 (Mon.) 12:30

Place : R517, New Physics Building, NTU

Abstract:

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 mA′ is not zero. This mixing can be large when mA′ is close to mZ even if the parameter ϵ is small. Many efforts have been made to constrain the parameter ϵ for a low dark photon mass mA′ compared with the Z boson mass mZ. We study the search for dark photon in e^+e^−→γA′→γμ+μ− for a dark photon mass mA′ as large as kinematically allowed at future e^+e^− colliders. For large mA′, 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≲mA′≲330 GeV, the 2σ 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 mA′≳50 GeV. For mA′≳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 5 ab−1 can be even better than that at 13~TeV LHC with 3 ab−1 for mA′≳180 GeV. We also comment on sensitivities of e^+e^− → γA with dark photon decay

into several other channels at future e^+e^− colliders.

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Chao-Jung Kuo

Administrative Staff, National Center for Theoretical Science (NCTS)

Phone: +886-2-3366-5566 , Fax: +886-2-3366-5565