THRESHOLD PRODUCTION OF HEAVY TOP QUARKS - QCD AND THE HIGGS BOSON

We calculate the threshold cross section for e+e- --> ttBAR to leading-logarithmic order in QCD, using a nonrelativistic approximation suggested by Fadin and Khoze. We study the mass range 100 less-than-or-equal-to m(t) less-than-or-equal-to 250 GeV, and show that the cross section is an excellent measure of alpha-s for the lower portion of the mass range, while for a heavier top quark it is sensitive to the mass and couplings of the Higgs boson. We argue that a precise determination of m(t) and a measurement of GAMMA-t are possible. We also show that nonperturbative effects are small, confirming that the ttBAR threshold is a detailed perturbative test of the standard model.