[Paper Review] Second order QCD corrections to gluonic jet production at hadron colliders

James Currie, A. Gehrmann–De Ridder+4 more|arXiv (Cornell University)|Jul 21, 2014

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper presents the first numerical results for next-to-next-to-leading order (NNLO) QCD corrections to gluonic dijet production at hadron colliders, focusing on the leading-color $q\bar{q} \to gg$ subprocess using the NNLOJET framework. It demonstrates that NNLO corrections increase the dijet cross section by 16–27% compared to NLO, with significant scale dependence and improved precision for global PDF and $\alpha_s$ fits at the LHC.

ABSTRACT

We report on the calculation of the next-to-next-to-leading order (NNLO) QCD corrections to the production of two gluonic jets at hadron colliders. In previous work, we discussed gluonic dijet production in the gluon-gluon channel. Here, for the first time, we update our numerical results to include the leading colour contribution to the production of two gluonic jets via quark-antiquark scattering.

Motivation & Objective

• To compute next-to-next-to-leading order (NNLO) QCD corrections for gluonic dijet production in the $q\bar{q} \to gg$ channel at hadron colliders.
• To extend previous NNLO results on the $gg \to gg$ channel to include the leading-color $q\bar{q} \to gg$ subprocess, which is dominant at high $p_T$.
• To provide fully differential cross sections for inclusive and dijet observables at NNLO, enabling precision comparisons with LHC data.
• To quantify the size of higher-order QCD effects on jet production, reducing theoretical uncertainties in $\alpha_s$ and PDF determinations.
• To lay the foundation for future inclusion of the $qg$ channel and full-color $2\to 2$ dijet processes at NNLO.

Proposed method

• Employed the antenna subtraction method to handle infrared singularities in virtual and real radiation corrections at NNLO.
• Used the NNLOJET parton-level generator to compute fully differential cross sections for inclusive and dijet observables.
• Applied the anti-$k_T$ jet algorithm with $R=0.7$ and standard jet selection cuts: $p_T > 80$ GeV, $|y| < 4.4$, and $p_{T2} > 60$ GeV for dijets.
• Set factorization and renormalization scales dynamically to $\mu = p_{T1}$ for each event to minimize scale dependence.
• Combined results from $gg \to gg$ and $q\bar{q} \to gg$ channels, with the former dominating the total cross section.
• Performed numerical integration over phase space using sector decomposition and iterative subtraction techniques to handle UV and IR divergences.

Experimental results

Research questions

• RQ1 What is the size of the NNLO QCD corrections to the $q\bar{q} \to gg$ subprocess in dijet production at the LHC?
• RQ2 How do NNLO corrections affect the inclusive jet transverse momentum distribution and dijet invariant mass spectrum?
• RQ3 What is the impact of the $q\bar{q} \to gg$ channel on the total dijet cross section compared to the $gg \to gg$ channel?
• RQ4 How do the $k$-factors (NNLO/NLO) vary with $p_T$, rapidity, and dijet mass?
• RQ5 To what extent do NNLO corrections reduce theoretical uncertainties in $\alpha_s$ and PDF fits using jet data?

Key findings

• The NNLO/NLO $k$-factor for the inclusive jet cross section is approximately 1.27 at low $p_T$ and 1.16 at high $p_T$, indicating a 16–27% increase over NLO.
• For the $q\bar{q} \to gg$ channel alone, the NNLO/NLO $k$-factor is about 1.05, corresponding to a 5% correction.
• The doubly differential $k$-factor for $d^2\sigma/dp_T d|y|$ remains relatively flat across rapidity bins, with corrections between 16% and 27% depending on $p_T$.
• The dijet invariant mass distribution shows a NNLO/NLO $k$-factor of 1.25 at low $m_{jj}$, decreasing to 1.13 at moderate $m_{jj}$, and rising to 1.20 at high $m_{jj}$.
• The corrections are consistent across different rapidity slices, indicating robustness of the NNLO results in central and forward jet regions.
• The $gg \to gg$ channel dominates the total dijet cross section, but the $q\bar{q} \to gg$ contribution is essential for full-color accuracy and future global fits.