Search for direct top squark pair production in final states with two leptons in root 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˜ 0 1 , the decay t ˜ → tχ˜ 0 1 into an on-shell top quark and the lightest neutralino, the three-body decay t ˜ → bWχ˜ 0 1 and the four-body decay t ˜ → bνχ˜ 0 1 . 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˜ 0 1 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