Measurement of the inclusive 3-jet production differential cross section in proton-proton collisions at 7 TeV and determination of the strong coupling constant in the TeV range

TL;DR

The paper reports a CMS measurement of the inclusive 3-jet differential cross section at 7 TeV, using 5 fb^-1 of data and focusing on the three leading jets. The cross section, expressed as d^2σ/(dm3 dy_max), is unfolded to correct detector effects and compared to NLO pQCD predictions with various PDFs and nonperturbative corrections, enabling a precise extraction of α_S(MZ). A combined fit for m3 > 664 GeV yields α_S(MZ) = 0.1171 with quantified experimental, PDF, NP, and scale uncertainties, and the running α_S(Q) is probed up to ~1.4 TeV. The results are consistent with the world average and prior CMS determinations, and extend tests of QCD to higher energy scales. This work reinforces the validity of perturbative QCD in multijet production and provides a high-scale constraint on the strong coupling constant.

Abstract

This paper presents a measurement of the inclusive 3-jet production differential cross section at a proton-proton centre-of-mass energy of 7 TeV using data corresponding to an integrated luminosity of 5 inverse femtobarns collected with the CMS detector. The analysis is based on the three jets with the highest transverse momenta. The cross section is measured as a function of the invariant mass of the three jets in a range of 445-3270 GeV and in two bins of the maximum rapidity of the jets up to a value of 2. A comparison between the measurement and the prediction from perturbative QCD at next-to-leading order is performed. Within uncertainties, data and theory are in agreement. The sensitivity of the observable to the strong coupling constant alpha[S] is studied. A fit to all data points with 3-jet masses larger than 664 GeV gives a value of the strong coupling constant of alpha[S](MZ) = 0.1171 +/- 0.0013 (exp) +0.0073/-0.0047 (theo).

Figures (7)

• Figure 1: Overview of the measurement uncertainties in the inner $\lvert y \rvert_{\text{max}}\xspace < 1$ (top) and the outer rapidity region $1 \leq \lvert y \rvert_{\text{max}}\xspace < 2$ (bottom). All uncertainty components, including the 1% uncorrelated residual uncertainty, are added in quadrature to give the total uncertainty.
• Figure 2: Overview of the NP correction factors and their uncertainties in the inner $\lvert y \rvert_{\text{max}}\xspace < 1$ (solid line) and in the outer rapidity region $1 \leq \lvert y \rvert_{\text{max}}\xspace < 2$ (dashed line).
• Figure 3: Overview of the theory uncertainties in the inner $\lvert y \rvert_{\text{max}}\xspace < 1$ (top) and in the outer rapidity region $1 \leq \lvert y \rvert_{\text{max}}\xspace < 2$ (bottom) for the CT10 PDF set with NLO PDF evolution.
• Figure 4: Comparison of the measured 3-jet mass cross section with the theory prediction for the two regions in $\lvert y \rvert_{\text{max}}$. This prediction is based on an NLO 3-jet calculation, which employs the CT10-NLO PDF set and is corrected for nonperturbative effects. The vertical error bars represent the total experimental uncertainty, while the horizontal error bars indicate the bin widths.
• Figure 5: Ratio of the 3-jet mass cross section, divided by NP corrections, to the theory prediction at NLO with the CT10-NLO (top) or CT10-NNLO PDF set (bottom) for the inner rapidity region (left) and for the outer rapidity region (right). The data are shown with error bars representing the statistical uncertainty after unfolding added quadratically to the 1% uncorrelated residual uncertainty and gray rectangles for the total correlated systematic uncertainty. The light gray (colour version: yellow) band indicates the PDF uncertainty for the CT10 PDF sets at 68% confidence level. In addition, the ratios of the NLO predictions are displayed for the PDF sets MSTW2008, NNPDF2.1, HERAPDF1.5, and ABM11, also at next-to- (top) and next-to-next-to-leading evolution order (bottom).