Search for Direct Top Squark Pair Production in Final States with Two Leptons in √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 opposite-charge leptons (electrons or muons) are reported, using 36.1 fb⁻¹ of integrated luminosity from proton-proton collisions at √s = 13 TeV collected by the ATLAS detector at the Large Hadron Collider. To cover a range of mass differences between the top squark t˜ and lighter supersymmetric particles, four possible decay modes of the top squark are targeted with dedicated selections: the decay t˜→ bχ˜₁(±) into a b-quark and the lightest chargino with χ˜₁(±) Wχ˜₁⁰,the decay t˜ → tχ˜₁⁰ into an on-shell top quark and the lightest neutralino, the three-body decay t˜ → bW χ˜₁⁰ and the four-body decay t˜ → bℓνχ˜₁⁰. No significant excess of events is observed above the Standard Model background for any selection, and limits on top squarks are set as a function of the t˜ and χ˜₁⁰ masses. The results exclude at 95% confidence level t˜ masses up to about 720 GeV, extending the exclusion region of supersymmetric parameter space covered by previous searches.