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

We present a search for direct top squark production in the opposite-sign dilepton channel using LHC pp collision data at $\sqrt{s}=13~\mathrm{TeV}$ amounting to $12.9~\mathrm{fb}^{-1}$ 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, 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 a simplified supersymmetric model with pair production of top squarks that each decay to a top quark and a neutralino. For neutralino masses below $150~\mathrm{GeV}$, masses of the lightest top squark below $650~\mathrm{GeV}$ are excluded at a confidence level of $95\%$.