Search for phenomena beyond the Standard Model in events with large $b$-jet multiplicity using the ATLAS detector at the LHC

A search is presented for new phenomena in final state events characterized by high jet multiplicity, no isolated leptons (electrons and muons), and large multiplicity of jets originating from the fragmentation of $b$-quarks ($b$-jets). The search uses 139 fb$^{-1}$ of $\sqrt{s}$ = 13 TeV proton--proton collision data collected by the ATLAS experiment at the Large Hadron Collider during Run 2. The dominant source of background, namely multijet production, is estimated using a data-driven technique based on the extrapolation from events with low $b$-jet multiplicity to the events with high $b$-jet multiplicity used in the search. No significant excess over the Standard Model expectation is observed and 95% confidence-level limits are extracted constraining simplified models of R-parity-violating supersymmetry that feature top-squark pair production. The exclusion limits reach up to 950 GeV in top-squark mass in the models considered.