FINAL-STATE INTERACTIONS IN E(-)-]T(T)OVER-BAR-]BL(+)NU(B)OVER-BARW(-) NEAR THE TOP-QUARK THRESHOLD()E()

We calculate final-state interaction corrections to the energy-angular distribution of l(+) in semileptonic top quark decay, where the paren t top quark is produced via e(+)e(-)-->t (t) over bar near threshold. These are the corrections due to gluon exchange between t and (b) over bar((t) over bar and b) and between b and (b) over bar. Combining wit h other previously known corrections, we explicitly write down the l() energy-angular distribution including the full O(alpha(s)) = O(beta) corrections near the t (t) over bar threshold. Numerical analyses of the final-state interaction corrections are given. We find that they d eform the l(+) distribution typically at the 10% level. We also find t hat all qualitative features of the numerical results can be understoo d from intuitive pictures. The mechanisms of various effects of the fi nal-state interactions are elucidated. Finally we define an observable which is proper to the decay process of the top quark (dependent only on d Gamma(t-->bl+v)/dE(1)d Omega(1) of a free polarized top quark) n ear the t (t) over bar threshold. Such a quantity will be useful in ex tracting the decay properties of the top quark using the highly polari zed top quark samples.