Search for new phenomena in final states with two leptons and one or no $b$-tagged jets at $\sqrt{s} = 13$ TeV using the ATLAS detector

A search for new phenomena is presented in final states with leptons and $b$-tagged jets selections. The selection includes two opposite-sign leptons (electrons or muons) with large invariant mass and no $b$-tagged jets or exactly one $b$-tagged jet. The analysis is based on the full LHC Run-2 proton--proton collision dataset at a centre-of-mass energy of $\sqrt{s} = 13$ TeV, corresponding to an integrated luminosity of 139 fb$^{-1}$ recorded by the ATLAS experiment. No significant deviation from the expected background is observed in the data. A four-fermion contact interaction between two quarks ($b,s$) and two leptons ($ee$ or $\mu\mu$), inspired by the $B$-meson decay anomalies, is used as a benchmark signal model. This model is characterized by the energy scale and coupling, $\Lambda$ and $g_*$, respectively. Contact interactions with $\Lambda / g_*$ lower than 2.0 (2.4) TeV are excluded for electrons (muons) at the 95% confidence level, still far from the value which is favored by the $B$-meson decay anomalies. In addition, model-independent limits are set as a function of the selection on the di-lepton invariant mass, which allows for the reinterpretation of the results in terms of other signal scenarios.