Measurement of azimuthal correlations among jets and determination of the strong coupling in pp collisions at $\sqrt{s}=13~\mathrm{TeV}$

A measurement is presented of the ratio observable $R_{\Delta\phi}(p_\mathrm{T})$ that provides a measure of the azimuthal correlations among jets with large transverse momentum $p_\mathrm{T}$. The $R_{\Delta\phi}(p_\mathrm{T})$ variable is defined as the ratio of the number of neighbouring jets in events with a 3-jet topology, enforced through an azimuthal angular separation of $2\pi/3<\Delta\phi<7\pi/8$, over the number of inclusive jets within the same jet $p_\mathrm{T}$ bin. The $R_{\Delta\phi}(p_\mathrm{T})$ variable is measured over the $p_\mathrm{T} \approx 360\mathord{-}3200~\mathrm{GeV}$ range 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 $134~\mathrm{fb}^{-1}$. The results are compared to predictions from Monte Carlo event generator simulations that include parton showers, hadronisation, and multiparton interactions. Fixed-order predictions of perturbative quantum chromodynamics (pQCD) at next-to-leading-order (NLO) accuracy obtained with the NNPDF3.1 NLO parton densities, corrected for nonperturbative and electroweak effects, are also compared to the measurement. Within uncertainties, data and theory are in agreement. From this comparison, the strong coupling constant at the Z boson mass scale is determined to be $\alpha_S(M_{\mathrm{Z}})=0.1177 \pm 0.0013\, \text{(exp)} _{-0.0073}^{+0.0116} \, \text{(th)} = 0.1177_{-0.0074}^{+0.0117}$, where the total uncertainty is dominated by the scale dependence of the fixed-order predictions. A test of the running of $\alpha_S(Q)$ in the TeV region shows no deviation from the expected pQCD behaviour.