# NLO QCD predictions for $t\bar{t}b\bar{b}$ production in association with a light jet at the LHC

## TL;DR

This paper presents NLO QCD predictions for ttbb production with an additional jet at the LHC, providing detailed analysis of uncertainties, QCD radiation patterns, and benchmarks to improve modeling accuracy for Higgs measurements.

## Contribution

It introduces a systematic scale alignment method for NLO calculations of ttbbj, enhancing the understanding of uncertainties and QCD radiation effects in ttbb production.

## Key findings

- Scale uncertainties are 20-30% for cross sections and below 10% for distribution shapes.
- QCD recoil effects significantly influence the kinematics of the ttbb system.
- Adjusting QCD scales can reduce the large NLO K-factor in ttbb cross section.

## Abstract

Theoretical predictions for ttbb production are of crucial importance for ttH measurements in the H->bb channel at the LHC. To address the large uncertainties associated with the modelling of extra QCD radiation in ttbb events, in this paper we present a calculation of pp->ttbbj at NLO QCD. The behaviour of NLO corrections is analysed in a variety of observables, and to assess theoretical uncertainties we use factor-two rescalings as well as different dynamic scales. In this context, we propose a systematic alignment of dynamic scales that makes it possible to disentangle normalisation and shape uncertainties in a transparent way. Scale uncertainties at NLO are typically at the level of 20-30% in fiducial cross sections, and below 10% for the shapes of distributions. The kinematics of QCD radiation is investigated in detail, including the effects of its recoil on the objects of the ttbb system. In particular, we discuss various azimuthal correlations that allow one to charaterise the QCD recoil pattern in a precise and transparent way. In general, the calculation at hand provides a variety of precise benchmarks that can be used to validate the modelling of QCD radiation in ttbb generators. Moreover, as we will argue, pp->ttbbj at NLO entails information that can be used to gain insights into the perturbative convergence of the inclusive ttbb cross section beyond NLO. Based on this idea, we address the issue of the large NLO K-factor observed in the ttbb cross section, and we provide evidence that supports the reduction of this K-factor through a mild adjustment of the QCD scales that are conventionally used for this process. The presented 2->5 NLO calculations have been carried out using OpenLoops 2 in combination with Sherpa and Munich.