Top-quark physics in six-quark final states at the Next Linear Collider

TL;DR

This paper analyzes six-quark production with a $bar b$ pair at the Next Linear Collider, highlighting electroweak backgrounds, Higgs mass dependence, and the impact of initial-state radiation on event-shape variables like thrust.

Contribution

It provides a complete electroweak calculation of six-quark final states, emphasizing the significance of backgrounds and initial-state radiation effects in top-quark studies.

Findings

Electroweak backgrounds are about 10% above the $t\bar t$ threshold.

Cross-section varies by ~10% with Higgs mass between 100 and 185 GeV.

Initial-state radiation significantly affects event-shape variables like thrust.

Abstract

The processes of six-quark production with one $b\bar b$ pair are studied by means of a complete tree-level electroweak calculation. The top-quark signal is examined: the importance of electroweak backgrounds, of the order of 10% above the $t\bar t$ threshold and of about 30% of the purely electroweak signal at threshold, is further stressed by studying the dependence of the cross-section at threshold on the Higgs mass in the range between 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 radiation 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 authors, is confirmed also in the presence of electroweak backgrounds and initial-state radiation.