NNLO QCD subtraction for top-antitop production in the $q\bar{q}$ channel

TL;DR

This paper develops a method for precise NNLO QCD calculations of top-antitop production in the quark-antiquark channel, utilizing antenna subtraction and OpenLoops for stable amplitude computation.

Contribution

It introduces an extension of the antenna subtraction formalism for massive colored particles and demonstrates its effectiveness in NNLO top-antitop production calculations.

Findings

Successful computation of double real and real-virtual contributions

High numerical stability of amplitudes in soft and collinear regions

Effective subtraction terms that approximate matrix elements in singular limits

Abstract

We present the computation of the double real and real-virtual contributions to top-antitop pair production in the quark-antiquark channel at leading colour. The $q \bar q \to t \bar{t} g$ amplitudes contributing to the real-virtual part are computed with OpenLoops, and their numerical stability in the soft and collinear regions is found to be sufficiently high to perform a realistic NNLO calculation in double precision. The subtraction terms required at real-real and real-virtual levels are constructed within the antenna subtraction formalism extended to deal with the presence of coloured massive final state particles. We show that those subtraction terms approximate the real-real and real-virtual matrix elements in all their singular limits.