Measurement of dijet angular distributions and search for beyond the standard model physics in proton-proton collisions at $\sqrt{s}$ = 13 TeV

A measurement is presented of dijet angular distributions in proton-proton collisions at $\sqrt{s}$ = 13 TeV, using data collected with the CMS detector at the CERN LHC and corresponding to an integrated luminosity of 138 fb$^{-1}$. For the first time, the dijet angular distributions, corrected for detector effects, are compared with the predictions of perturbative quantum chromodynamics at next-to-next-to-leading order, including next-to-leading-order electroweak corrections. While data are generally found to be in agreement with predictions, a small difference in shape of the normalized distributions is seen for dijet masses ranging from 2.4 to 4.8 TeV and above 6 TeV. The distributions are used to search for proposed signatures of quark compositeness, extra spatial dimensions, quantum black holes, dark-matter mediators, axion-like particles, and anomalous gluon couplings. The most stringent limits to date are set for most of these scenarios. Quark contact interactions are excluded at 95% confidence level (CL) up to a scale of 17 (37) TeV for destructive (constructive) interference in a benchmark scenario, valid to next-to-leading order in quantum chromodynamics, and in which only left-handed quarks participate. The coupling of axion-like particles to the gluon, $c_{\text{g}}/f_{\text{a}}$, is constrained to be lower than 0.42 TeV$^{-1}$ at 95% CL. The anomalous triple-gluon coupling, $C_{\text{G}}/Λ^2$, in a standard model effective field theory is constrained to be lower than 0.0076 TeV$^{-2}$ at 95% CL.