Z decays to top quarks

Z decays to top quark pairs — if kinematically possible — will provide an accurate measurement of the top-quark mass in e+e− collisions. We study various distributions of leptons and jets in the final state for semileptonic quark decays. Fragmentation and polarization effects are analyzed. In addition to large longitudinal and transverse polarizations, a small normal t-quark polarization is built up by γ,Z interference and perturbative QCD corrections. We comment also briefly on polarization effects in the tb decays of W bosons that are hadronically produced.