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 $36.1{\text{fb}}^{-1}$ of integrated luminosity from proton-proton collisions at $\sqrt{s}=13$ TeV collected by the ATLAS detector at the Large Hadron Collider. 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 $\tilde{t}\to b{\tilde{\chi }}_1^{\pm }$ into a b-quark and the lightest chargino with ${\tilde{\chi }}_1^{\pm }\to W{\tilde{\chi }}_1^0$ , the decay $\tilde{t}\to t{\tilde{\chi }}_1^0$ into an on-shell top quark and the lightest neutralino, the three-body decay $\tilde{t}\to bW{\tilde{\chi }}_1^0$ and the four-body decay $\tilde{t}\to b\ell \nu {\tilde{\chi }}_1^0$ . 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 $\tilde{t}$ and ${\tilde{\chi }}_1^0$ masses. The results exclude at 95% confidence level $\tilde{t}$ masses up to about 720 GeV, extending the exclusion region of supersymmetric parameter space covered by previous searches.