Measurement of multijet azimuthal correlations and determination of the strong coupling in proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This paper measures azimuthal correlations among high-$p_T$ jets in proton-proton collisions at 13 TeV to determine the strong coupling constant and test its running, finding good agreement with NLO pQCD predictions.

Contribution

It provides a novel measurement of a ratio observable related to jet azimuthal correlations at high energies, extracting the strong coupling constant with improved precision.

Findings

Measured $ ext{α}_ ext{S}(m_Z)$ = 0.1177 ± 0.0013 (exp) ± 0.0074 (theo)

Data agrees with NLO pQCD predictions within uncertainties

No deviation observed in the running of $ ext{α}_ ext{S}$ in the TeV region

Abstract

A measurement is presented of a ratio observable that provides a measure of the azimuthal correlations among jets with large transverse momentum $p_\mathrm{T}$. This observable is measured in multijet events over the range of $p_\mathrm{T}$ = 360-3170 GeV based on data collected by the CMS experiment in proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 134 fb$^{-1}$. The results are compared with predictions from Monte Carlo parton-shower event generator simulations, as well as with fixed-order perturbative quantum chromodynamics (pQCD) predictions at next-to-leading-order (NLO) accuracy obtained with different parton distribution functions (PDFs) and corrected for nonperturbative and electroweak effects. Data and theory agree within uncertainties. From the comparison of the measured observable with the pQCD prediction obtained with the NNPDF3.1 NLO PDFs, the strong coupling at the Z boson mass scale is $\alpha_\mathrm{S}(m_\mathrm{Z})$ = 0.1177 $\pm$ 0.0013 (exp) $_{-0.0073}^{+0.0116}$ (theo) = 0.1177 $_{-0.0074}^{+0.0117}$, where the total uncertainty is dominated by the scale dependence of the fixed-order predictions. A test of the running of $\alpha_\mathrm{S}(m_\mathrm{Z})$ in the TeV region shows no deviation from the expected NLO pQCD behaviour.