Decay-lepton angular distributions in e+e−→tt to O(αs) in the soft-gluon approximation

Order-αs QCD corrections in the soft-gluon approximation to angular distributions of decay charged leptons in the process e+e−→tt, followed by semileptonic decay of t or t, are obtained in the e+e− centre-of-mass frame. As compared to distributions in the top rest frame, these have the advantage that they would allow direct comparison with experiment without the need to reconstruct the top rest frame or a spin quantization axis. Analytic expressions for the distribution in the charged-lepton polar angle, and triple distribution in the polar angle of t and polar and azimuthal angles of the lepton are obtained. Numerical values for the polar-angle distributions of charged leptons are discussed for s=400 GeV and 800 GeV.