Search for paired dijet resonances

A data-driven search for pairs of dijet resonances with identical mass is conducted in final states with at least four jets, and results are presented for both resonant and non-resonant production modes. The search uses 138 fb$^{-1}$ of integrated luminosity collected by the CMS detector in proton-proton collisions at $\sqrt{s}=$ 13 TeV. Distributions of the four-jet mass above 1.6 TeV, and average dijet mass above 0.35 TeV, are fit with functions to determine the backgrounds. Model independent limits, at 95 $\%$ confidence level, are reported on the production cross section of four-jet and dijet resonances. These first LHC limits on resonant pair production at high mass, are applied to a signal model of diquarks that decay into pairs of vector-like quarks, excluding diquark masses below 7.6 TeV for a particular model scenario. There are two events on the tail of the distributions, with a four-jet mass of 8 TeV and an average dijet mass of 2 TeV, resulting in a local significance of 3.9 standard deviations and a global significance of 1.6 standard deviations if interpreted as a signal. The non-resonant search excludes pair production of top squarks with masses between 0.50 and 0.52 TeV, and between 0.58 and 0.77 TeV, for supersymmetric R-parity-violating decays to quark pairs, significantly extending previous limits. Here, the most significant signal hypothesis occurs at an average dijet mass of 0.95 TeV, for which the local significance is 3.6 standard deviations and the global significance is 2.5 standard deviations.