The study of neutral triple gauge couplings in the process e+e- → Zγ including unitarity bounds

The neutral triple gauge couplings (nTGCs) provide a unique opportunity to probe new physics beyond the Standard Model. The nTGCs can be described by an effective field theory (EFT), which is valid only under a certain energy scale. One of the signatures that an EFT is no longer valid is the violation of unitarity. We study the partial wave unitarity bounds on the coefficients of nTGCs in the process e(+)e(-) -> Z gamma. In the experiments, the constraints obtained should be tighter than the unitarity bounds, otherwise the results are meaningless, therefore there exists a minimal luminosity for a e(+)e(-) collider such as the CEPC to study the nTGCs. To derive the minimal luminosity, the kinematic features and event selection strategy are studied by Monte-Carlo simulation. Both the processes e(+)e(-) -> l(+)l(-)gamma and e(+)e(-) -> jj gamma are studied, event selection strategies are discussed. Based on the statistical significance, the expected constraints in experiments are estimated. The required luminosities for the experiments to reach the unitarity bounds are presented. (C) 2021 The Authors. Published by Elsevier B.V.

Automated summary

The neutral triple gauge couplings (nTGCs) provide an unique opportunity to probe new physics beyond the Standard Model, which can be described by effective field theory valid under certain energy scale, and the coefficients of nTGCs in the process e(+)e(-) -> Z gamma should be constrained by partial wave unitarity bounds, with experimentally obtained results tighter than unitarity bounds to be meaningful.