Multi-differential measurement of the dijet cross section in proton-proton collisions at $\sqrt{s} = 13\,TeV$

A measurement of the dijet production cross section is reported based on an integrated luminosity of $36.3\ fb^{-1}$ of proton-proton collision data collected in 2016 at $\sqrt{s} = 13\ TeV$ by the CMS detector at the CERN LHC. Jets are reconstructed with the anti-kT algorithm for distance parameters of $R = 0.4$ and $R = 0.8$ and differential cross sections are measured as a function of the kinematic properties of the two jets with largest transverse momenta $p_T$. Double-differential (2D) measurements are presented as a function of the largest absolute rapidity $y_{max}$ of the two jets and the dijet invariant mass $m_{1,2}$. Triple-differential (3D) measurements are presented as a function of the dijet rapidity separation $y*$ , the total boost $y_b$ of the dijet system, and either $m_{1,2}$ or the average dijet transverse momentum $\langle p_T\rangle_{1,2}$ as the third variable. The measured cross sections are unfolded to correct for detector effects and are compared with fixed-order calculations derived at next-to-next-to-leading order in perturbative quantum chromodynamics. The impact of the 2D and 3D measurements is investigated on the determination of the parton distribution functions (PDFs) and the strong coupling constant ($\alpha_S$), with the inclusion of the 3D cross sections yielding the more precise value of $\alpha_S(m_Z) = 0.1201 \pm 0.0020$.