  New particles with large masses that decay into hadronically interacting
particles are predicted by many models of physics beyond the Standard Model. A
search for a massive resonance that decays into pairs of dijet resonances is
performed using 140 fb$^{-1}$ of proton$-$proton collisions at $\sqrt{s}=13$
TeV recorded by the ATLAS detector during Run 2 of the Large Hadron Collider.
Resonances are searched for in the invariant mass of the tetrajet system, and
in the average invariant mass of the pair of dijet systems. A data-driven
background estimate is obtained by fitting the tetrajet and dijet invariant
mass distributions with a four-parameter dijet function and a search for local
excesses from resonant production of dijet pairs is performed. No significant
excess of events beyond the Standard Model expectation is observed, and upper
limits are set on the production cross-sections of new physics scenarios.
