Search for dark matter in association with a $\mathrm{t\overline{t}}$ pair at $\sqrt{s}=13~\mathrm{TeV}$ in the dilepton channel with 2016 data

A search is performed for dark matter produced in association with $\mathrm{t\overline{t}}$ pairs in data from proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC. The data corresponds to $35.9~\mathrm{fb}^{-1}$ collected with the CMS detector in 2016. The analysis looks for an excess of events with large imbalance in transverse momentum and a top quark pair decaying in the dileptonic mode. The results are interpreted in the context of simplified models of dark matter production. Assuming unitary coupling values to standard model (SM) particles $g_{\text{q}}$, and dark matter (DM) particles $g_{\chi}$, and DM mass $m_{\chi} = 1~\mathrm{GeV}$, the observed (expected) $95\%$ CL exclusions for a scalar mediator are $m_{\phi} < 74\:(99)~\mathrm{GeV}$. The $95\%$ CL exclusion expected for a pseudoscalar mediator is $m_{a} < 50~\mathrm{GeV}$, while none is observed.