Next-to-leading order QCD corrections to five jet production at the LHC

TL;DR

This paper delivers the first next-to-leading order QCD predictions for proton-proton collisions producing five jets at the LHC, using an automated unitarity-based approach for one-loop amplitudes (NJet) interfaced with Sherpa for real emissions and subtraction. Employing a dynamical HT-based scale and anti-kt jet clustering, the authors show that NLO corrections reduce scale uncertainties and provide improved agreement with ATLAS data for higher jet multiplicities. They analyze partonic-channel contributions and jet-rate ratios, finding that the 4/3 and 5/4 ratios are perturbatively stable and suitable for potential αs extractions, while exploring PDF uncertainties across distributions. The results advance precision QCD in high-multiplicity final states and offer benchmarks for PDF and αs studies using multi-jet LHC data.

Abstract

We present theoretical predictions for five jet production in proton-proton collisions at next-to-leading order accuracy in QCD. Inclusive as well as differential observables are studied for collision energies of 7 and 8 TeV. In general the next-to-leading order corrections stabilize the theoretical predictions with respect to scale variations. In case of the inclusive jet cross sections, we compare with experimental data where possible and find reasonable agreement. We observe that the four-to-three and five-to-four jet ratios show better perturbative convergence than the known three-to-two ratio and are promising candidates for future alpha_s measurements. Furthermore, we present a detailed analysis of uncertainties related to parton distribution functions. The full colour virtual matrix elements used in the computation were obtained with the NJet package, a publicly available library for the evaluation of one-loop amplitudes in massless QCD.

Figures (25)

• Figure 1: Same as Fig. \ref{['fig:5j_scalevar']} but using the NLO setup in LO.
• Figure 2: Residual scale dependence of the 5-jet cross section in leading and next-to-leading order.
• Figure 3: Cross sections for 2-, 3-, 4-, 5- and 6-jet production in leading and next-to-leading order as calculated with NJet as well as results from ATLAS measurements Aad:2011tqa. All LO quantities use NNPDF2.1 with $\alpha_s(M_Z) = 0.119$. NLO quantities use NNPDF2.3 with $\alpha_s(M_Z) = 0.118$, the 6-jet cross section is only avaiable LO accuracy.
• Figure 4: Theoretical predictions for the jet ratios ${\cal{R}}_n$ compared with recent ATLAS measurements Aad:2011tqa. Theoretical predictions are made with the central values of the 4 listed PDF sets with NLO $\alpha_s$ running. $\alpha_s(m_Z) = 0.118$ for NNPDF2.3, CT10 and ABM11 and $\alpha_s(m_Z) = 0.120$ for MSTW2008
• Figure 5: The 3/2 jet ratio as a function of the $p_T$ of the leading jet. ATLAS data is taken from Aad:2011tqa. The cuts are given in section \ref{['sec:numsetup']} except the jet cone radius which is taken as $R=0.6$.