The ZZγ triple neutral gauge couplings are absent in the Standard Model (SM) at the tree level. They receive no contributions from dimension-6 effective operators, but can arise from effective operators of dimension-8. We study the scale of new physics associated with such dimension-8 operators that can be probed by measuring the reaction e+e−→Zγ followed by Z→ℓˉℓ,νˉν decays, at future e+e− colliders including the CEPC, FCC-ee, ILC and CLIC. We demonstrate how angular distributions of the final-state mono-photon and leptons can play a key rôle in suppressing SM backgrounds. We further demonstrate that using electron/positron beam polarizations can significantly improve the signal sensitivities. We find that the dimension-8 new physics scale can be probed up to the multi-TeV region at such lepton colliders.

Key words: neutral triple gauge coupling , beyond Standard Model , e+e− colliders

Full-text link:   http://hepnp.ihep.ac.cn/article/doi/10.1088/1674-1137/44/6/063106