Top-quark pair production at high invariant mass: an NNLO soft plus virtual approximation

TL;DR

This paper presents a comprehensive NNLO QCD approximation for top-quark pair production at high invariant mass, improving accuracy in the boosted top regime and highlighting the importance of resummation effects.

Contribution

It introduces the most complete NNLO soft plus virtual approximation for top-pair invariant mass distribution, surpassing previous methods based solely on NNLL resummation.

Findings

Moderate enhancement of differential cross section at high invariant mass.

Approximation is valid up to corrections of order m_t^2/M^2.

Resummation remains crucial for highly boosted top quarks.

Abstract

We obtain a soft plus virtual approximation to the NNLO QCD contributions to the top-pair invariant mass distribution at hadron colliders. It is valid up to corrections of order m_t^2/M^2, with M the pair invariant mass. This is currently the most complete QCD calculation for a differential cross section in top-quark pair production, and is useful for describing the high invariant mass region characteristic of boosted top quarks. We use our results to construct an improved NNLO approximation for the pair invariant mass distribution and compare it with previous, less complete approximations based on logarithmic terms from NNLL soft-gluon resummation alone. We find that the new NNLO approximation produces moderate enhancements of the differential cross section compared to previous ones, the effect being slightly more important at low values of invariant mass than at high ones. On the other hand, at high values of invariant mass the new NNLO corrections are dominated by even higher-order effects included in NNLL soft-gluon resummation, reaffirming the need for resummation in describing the highly boosted regime.