Search for direct stop pair production in the dilepton final state at $\sqrt{s}=$13 TeV

A search for direct top squark production in the opposite-sign dilepton channel is presented, using LHC pp collision data at $\sqrt{s}=13~\mathrm{TeV}$ amounting to $35.9~\mathrm{fb}^{-1}$ collected by the CMS detector in 2016. The search is performed in final states with two leptons, electrons or muons, jets, of which at least one is b-tagged, and missing transverse momentum. Signal regions are defined using transverse mass variables as well as missing transverse energy, which efficiently separate the signal from the dominant top-quark pair background. No significant deviation from the background prediction is observed. Exclusion limits are set in the context of two different simplified supersymmetric models with pair production of top squarks. For top squarks that each decay to a top quark and a neutralino, masses of the lightest top squark below $800~\mathrm{GeV}$ are excluded at a confidence level of $95\%$ for neutralino masses below $350~\mathrm{GeV}$. Interpreting the results within an alternative model where the top squarks undergo a cascade decay through charginos and sleptons, top squarks with masses up to $1300~\mathrm{GeV}$ are excluded for neutralino masses of $400~\mathrm{GeV}$.