Irreducible QCD backgrounds to top searches in semi-leptonic final states at the Next Linear Collider

TL;DR

This paper precisely calculates the dominant QCD background processes at future electron-positron colliders for top quark searches, using advanced matrix element techniques to improve background discrimination.

Contribution

It provides exact parton-level calculations of QCD backgrounds using 2 -> 6 matrix elements with helicity amplitudes, aiding in more accurate background estimation.

Findings

Exact computation of QCD background processes at the parton level.

Identification of kinematic differences to distinguish signal from background.

Use of helicity amplitude techniques for complex matrix element calculations.

Abstract

At future electron-positron colliders, one of the largest irreducible backgrounds to top searches in the channel `4 jets + lepton + missing energy' comes from QCD events of order $\alpha_s^2$. We compute here such processes exactly at the parton level by resorting to 2 -> 6 matrix elements exploiting helicity amplitude techniques. We adopt a typical selection procedure based on the tagging of a high momentum and separated lepton. We finally outline kinematic differences between signal and background events that can be exploited to further reduce such a QCD noise.