Anomalous radiative decays in the Z0-toponium complex

Recent evidence suggests the top quark has a mass of around 40 GeV. Consequently, the toponium could be almost degenerate in mass with the Z0. Using standard heavy quark wave functions, the authors estimate the branching ratio into γee can be as large as 18%. The radiative coupling between Z0 and toponium also induces a hefty width (85 MeV) for toponium decay into light quarks. Such large couplings can account for a substantial fraction of the γee-bar events observed recently at the CERN collider. Although a near degeneracy affects the decay matrix for the Z0 -toponium complex, it plays a minimal role in the mass matrix itself, and the standard rho-parameter is left essentially unchanged