Compositeness signature of Z⁰ in the ll^-γ decay mode

Abstract

We analyze the anomalous Z⁰ decay events seen in recent experiments on Z⁰ searches within the framework of a composite model for the weak vector bosons; the model is characterized by a mass scale Λ_H G_F^-1/2. We assume a direct four-fermion V, A coupling between leptons and the fermionic constituents of the weak bosons, and calculate the branching ratio Γ(Z⁰→ll^-γ)/Γ(Z⁰→ll^-). We show that this branching ratio is determined by the relative strengths of the vector and axial-vector parts of the preon current; a large radiative branching ratio requires that the current be predominantly axial vector.