Probing Neutral Triple Gauge Couplings via $\mathbf{Z\gamma }({\mathbf{\ell }}^{+}{\mathbf{\ell }}^{-}\mathbf{\gamma })$ Production at ${\mathbf{e}}^{+}{\mathbf{e}}^{-}$ Colliders

Abstract

Neutral triple gauge couplings (nTGCs) are absent in the Standard Model (SM) and at the dimension-6 level in the Standard Model Effective Field Theory (SMEFT), arising first from dimension-8 operators. As such, they provide a unique window for probing new physics beyond the SM. These dimension-8 operators can be mapped to nTGC form factors whose structure is consistent with the spontaneously-broken electroweak gauge symmetry of the SM. In this work, we study the probes of nTGCs in the reaction $e^{+}{e}^{-}\to Z\gamma$ with $Z\to {\ell }^{+}{\ell }^{-}(\ell =e,\mu )$ at an $e^{+}{e}^{-}$ collider. We perform a detector-level simulation and analysis of this reaction at the Circular Electron Positron Collider (CEPC) with collision energy $\sqrt{s}=240$ GeV and an integrated luminosity of 20 ab${}^{-1}$. We present the sensitivity limits on probing the new physics scales of dimension-8 nTGC operators via measurements of the corresponding nTGC form factors.

Comments: Frontiers of Physics (in Press), 22 pages, 10 Figs and 10 Tables