Probing the Scale of New Physics in the $ZZ\gamma$ Coupling at $e^+e^-$ Colliders

Understand

The $ZZ\gamma$ 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 $e^+e^-\to Z\gamma$, followed by $Z \to \ell\bar{\ell},\nu\bar{\nu}$ decays, at future $e^+e^-$ colliders including the ILC, CEPC, FCC-ee and CLIC.
• We demonstrate how angular distributions of the final state mono-photon and leptons can play a key role in suppressing SM backgrounds.