Search for direct top squark pair production in final states with two leptons in √s=13 TeV pp collisions with the ATLAS detector

Abstract

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 → b˜χ ± 1 into a b-quark and the lightest chargino with ˜χ ± 1 → W ˜χ 0 1 , the decay ˜t → t ˜χ 0 1 into an on-shell top quark and the lightest neutralino, the three-body decay ˜t → bW ˜χ 0 1 and the four-body decay ˜t → b ν ˜χ 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.