QCD corrections to decay-lepton polar and azimuthal angular distributions in e⁺e⁻→tt̅ in the soft-gluon approximationin the soft-gluon approximation

Abstract

QCD corrections to order α_s in the soft-gluon approximation to angular distributions of decay charged leptons in the process e⁺ e⁻→tt̅, followed by semileptonic decay of t or t̅, 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. The results also do not depend on the choice of a spin quantization axis for t or t̅. Analytic expression for the triple distribution in the polar angle of t and polar and azimuthal angles of the lepton is obtained. Analytic expression is also derived for the distribution in the charged-lepton polar angle. Numerical values are discussed for √s=400, 800 and 1500 GeV.