STRUCTURE OF THE Z(0) RESONANCE AND THE PHYSICAL-PROPERTIES OF THE Z(0) BOSON

The proximity of multiparticle production thresholds means that the Z0 resonance is formed, not by a single particle, but by a ''multiplet'' of distinct Z0 bosons differing slightly in mass. The effects that these thresholds can have on the gauge-invariant pole expansion near the Z0 resonance are studied. It is shown how this expansion naturally yields physical quantities from which the mass and partial widths of the unstable Z0 bosons can be defined. The recent discussion on the definition of the Z0 boson mass is reviewed and commented upon, stressing the distinction between the renormalized and physical masses.