The Study Of Neutral Triple Gauge Couplings In The Process E⁺e^-?Z_? Including Unitarity Bounds

The search of new physics(NP)beyond the Standard Model(SM)is one of the current frontier problems in particle physics.As a model-independent approach for searching NP signals,the Standard Model Effective Field Theory(SMEFT)is more efficiently and thus has received wide attention in recent years.Theoretical studies have shown that for some processes,the involved high dimensional operators start from dimension-8.One such example is the process induced by neutral triple gauge couplings(nTGCs).Therefore,the study of nTGCs provides a unique opportunity to search and study NPs.In this thesis,we study the contribution of dimension-8 operators containing nTGCs in the process e+e-?Z? at e+e-colliders(e.g.,CEPC).Both the leptonic and hadronic decays of the Z boson are studied.With the help of kinematic analysis,the event selection strategy is proposed,and the expected constraints on the coefficients of dimension-8 operators at furture colliders are obtained.Unlike previous studies,this thesis considers the partial wave unitarity bounds.For an e+e-collider,the coefficients of high dimensional operators can be directly constrained by partial wave unitarity bounds,which are independent of the expected constraints given by the signal background analysis.On the one hand,the expected constraints in the experiments must be tighter than those obtained from unitarity,otherwise they are meanless.On the other hand,the expected constraints in the experiments depend on the luminosity.Therefore,to study nTGCs in experiments,a minimal luminosity is required to make the expected constraints tighter than those obtained from unitarity.In this thesis,the minimum luminosity required to study the nTGCs at furture colliders are presented.Other improvements include that,parton shower and detector simulation are considered in the signal background analysis,the polarization feature of the Z boson is investigated and a scheme to highlight the signal events using the angular distribution of leptons is proposed.