Measurement and phenomenology of azimuthal correlations in high transverse momentum multi-jet topologies in CMS at the center-of-mass energy of 13 TeV

This work addresses the measurements and phenomenology of the azimuthal separation ∆φ$_{12}$ between the jets with the largest transverse momenta ($p$$_{T}$) in multi-jet event topologies. The measurements are based on proton-proton collision data at the center-of-mass energy of 13 TeV recorded by the Compact Muon Solenoid (CMS) experiment in 2016, and correspond to an integrated luminosity of 35.9 fb$^{−1}$ . The measurements are performed in ranges of the leading jet transverse momentum ($p$$^{max}_{T}$), covering the range $p$$^{max}_{T}$ > 200 GeV. Special attention is given to the investigation of the Sudakov region 170$^{◦}$ < ∆φ$_{12}$ < 180$^{◦}$ in inclusive 2- and 3-jet event topologies. This region characterizes nearly back-to-back jet topologies and is sensitive to contributions from soft partonic radiation. The observables are compared to theoretical predictions based on matrix element (ME) calculation at leading and next-to-leading-order accuracy in perturbative quantum chromodynamics (pQCD) combined with parton showers (PS). Discrepancies of up to 15% are observed for ∆φ$_{12}$ > 177$^{◦}$ .The measurements are complemented with a wide phenomenological investigation of the PS impact and its subsequent combination with the ME calculation on the ∆φ$_{12}$ distribution.The measurements of ∆φ12 in nearly back-to-back jet topologies for inclusive 2- and 3-jet events are not simultaneously described by any of the theoretical models. Predictions using ME and PS at different accuracies in pQCD provide a similar description of the data.