Search for direct top squark pair production in final states with two leptons in $\sqrt{s} = 13$ TeV $pp$ collisions with the ATLAS detector

The results of a search for direct pair production of top-squarks in events with two leptons (electrons or muons) are reported. The search uses 36.1 fb$^{-1}$ of integrated luminosity from LHC $pp$ collisions at $\sqrt{s}=13$ TeV collected by the ATLAS detector. To cover a range of mass differences between the top squark $\tilde{t}$ and lighter supersymmetric particles, four possible decay modes of the top squark are targeted with dedicated selections: the decay $\tilde{t} \rightarrow b \tilde{\chi}_{1}^{\pm}$ into a $b$-quark and the lightest chargino, the decay $\tilde{t} \rightarrow t \tilde{\chi}_{1}^{0}$ into an on-shell top quark and the lightest neutralino, the three-body decay $\tilde{t} \rightarrow b W \tilde{\chi}_{1}^{0}$ and the four-body decay $\tilde{t} \rightarrow b \ell \nu \tilde{\chi}_{1}^{0}$. No significant excess of events is observed above the Standard Model background for any selection, and cross-section limits are interpreted in limits on the $\tilde{t}$ and $\tilde{\chi}_{1}^{0}$ masses, significantly extending previous results.