A model of the Z boson is elaborated from a revised quantum electrodynamic theory (RQED) by the author. The electromagnetic steady field is derived from a separable generating function with a convergent radial part, resulting in a vanishing net electric charge and a nonzero spin and rest mass. From the superposition of the solutions of two Z bosons with antiparallel spin directions, a model is further formed of a composite boson, the computed mass mC of which becomes connected with the mass of 91 GeV for each Z boson. This results in a composite boson which is likely to become identical with the heavy particle recently detected at CERN. Both these particles are thus lacking of net electric charge, magnetic field and spin, are purely electrostatic and highly unstable, and have masses close to the value of 125 GeV.