Framing energetic top-quark pair production at the LHC

TL;DR

This paper analyzes the different topologies of top-quark pair production at the LHC, emphasizing the significance of gluon splitting processes over the traditional back-to-back production at high energies.

Contribution

It introduces a simple classification method for top-quark pair production topologies and explores their prevalence and characteristics at high invariant masses.

Findings

Gluon splitting dominates top-quark pair production at high energies.

Traditional back-to-back topology is only a minority at TeV-scale momentum transfer.

Event classification reveals distinct features relevant for experimental analysis.

Abstract

Top-quark pair production is central to many facets of LHC physics. At leading order, the top and anti-top are produced in a back-to-back topology, however this topology accounts only for a minority of $t \bar t$ events with TeV-scale momentum transfer. The remaining events instead involve the splitting of an initial or final-state gluon to $t \bar t$. We provide simple quantitative arguments that explain why this is the case and examine the interplay between different topologies and a range of variables that characterise the event hardness. We then develop a method to classify the topologies of individual events and use it to illustrate our findings in the context of simulated events, using both top partons and suitably defined fiducial tops. For events with large $t \bar t$ invariant mass, we comment on additional features that have important experimental and theoretical implications.