Search for supersymmetry in final states with two same-sign or three leptons and jets using 36 fb−1 of s√=13 TeV pp collision data with the ATLAS detector

A search for strongly produced supersymmetric particles using signatures involving several energetic jets and either two isolated same-sign leptons ($e$ or $\mu$), or at least three isolated leptons, is presented. The analysis relies on $b$-tagged jets and missing transverse momentum, to achieve good 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 36.1 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. In models considering gluino pair production, gluino masses are excluded up to 1.85 TeV at 95\% confidence level. When bottom squarks are pair-produced and decay to $t\tilde\chi^\pm_{1}$, models with bottom squark masses below 700 GeV and light neutralinos are excluded at 95\% confidence level. In addition, model independent limits are set on a possible contribution of new phenomena to the signal region yields.