Top-quark physics in six-quark final states at the next linear collider

The processes of six-quark production with one <b(b)over bar> pair are stud ied by means of a complete tree-level electroweak calculation. The top-quar k signal is examined: the importance of electroweak backgrounds, of the ord er of 10% above the <t(t)over bar> threshold and of about 30% of the purely electroweak signal at threshold, is further stressed by studying the depen dence of the cross section at threshold on the Higgs mass in the range betw een 100 GeV and 185 GeV, and finding variations of the order of 10%. In the study of some event-shape variables, a strong effect of initial-state radi ation is found, in particular for the thrust distribution, which is studied for several centre-of-mass energies at the TeV scale. The effectiveness of cuts on the thrust for isolating QCD backgrounds, as pointed out by some a uthors, is confirmed also in the presence of electroweak backgrounds and in itial-state radiation. (C) 1999 Elsevier Science B.V. All rights reserved.