NLO QCD calculations with HELAC-NLO

TL;DR

This work surveys the HELAC-NLO framework for performing NLO QCD calculations, detailing the OPP-based virtual corrections and Catani-Seymour real-emission subtraction, along with automation and efficient color handling. It demonstrates the approach through a case study of ttbar plus two jets at the LHC, showing reduced scale uncertainties and characteristic changes in both total and differential cross sections at NLO. The results underscore the importance of NLO predictions for accurate backgrounds in Higgs searches and other new-physics analyses. The authors also chart future enhancements, including full top decays, non-resonant contributions, and electroweak counterterms, to broaden the framework's applicability.

Abstract

Achieving a precise description of multi-parton final states is crucial for many analyses at LHC. In this contribution we review the main features of the HELAC-NLO system for NLO QCD calculations. As a case study, NLO QCD corrections for tt + 2 jet production at LHC are illustrated and discussed.

Figures (4)

• Figure 1: Scale dependence of the total cross section for $pp \to t\bar{t} + 2 \hbox{jets}+X$ at the LHC with $\mu_R = \mu_F = \xi \dot \mu_0$, where $\mu_0 = m_t$. The blue dotted curve corresponds to the LO, the red solid to the NLO result whereas the green dashed to the NLO results with a jet veto of 50 GeV.
• Figure 2: Distribution of the di-jet invariant mass for $pp \to t\bar{t} + 2 \hbox{jets}+X$ at the LHC. The red solid line refers to the NLO results while the blue dotted one to the LO one.
• Figure 3: Distributions of the transverse momentum for the first hardest jet for $pp \to t\bar{t} + 2 \hbox{jets}+X$ at the LHC. The red solid line refers to the NLO results while the blue dotted one to the LO one.
• Figure 4: Distributions of the transverse momentum for the second hardest jet for $pp \to t\bar{t} + 2 \hbox{jets}+X$ at the LHC. The red solid line refers to the NLO results while the blue dotted one to the LO one.