Search for supersymmetry with two same-sign leptons or three leptons using 13.2 fb$^{−1}$ of $\sqrt{s} = 13$ TeV $pp$ collision data collected by the ATLAS detector

This note presents a search for strongly produced supersymmetric particles using signatures involving multiple energetic jets and either two isolated same-sign leptons ($e$ or $\mu$) or at least three isolated leptons. The analysis also utilises other observables, such as $b$-tagged jets or missing transverse momentum, to extend its sensitivity. A data sample of proton-proton collisions at $\sqrt{s}= 13$ TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to a total integrated luminosity of 13.2 fb$^{-1}$, is used for the search. No significant excess over the Standard Model expectation is observed. The results are interpreted in several simplified supersymmetric models featuring $R$-parity conservation and $R$-parity violation, extending the exclusion limits from previous searches.