Abstract
A search for new physics is presented in final states with two oppositely charged leptons (electrons or muons), jets identified as originating from b quarks, and missing transverse momentum ($p_\mathrm{T}^\text{miss}$). The search uses proton-proton collision data at $\sqrt{s}=$ 13 TeV amounting to 35.9 fb$^{-1}$ of integrated luminosity collected using the CMS detector in 2016. Hypothetical signal events are efficiently separated from the dominant $\mathrm{t}\overline{\mathrm{t}}$ background with requirements on $p_\mathrm{T}^\text{miss}$ and transverse mass variables. No significant deviation is observed from the expected background. Exclusion limits are set in the context of simplified supersymmetric models with pair-produced top squarks. For top squarks, decaying exclusively to a top quark and a neutralino, exclusion limits are placed at 95% confidence level on the mass of the lightest top squark up to 800 GeV and on the lightest neutralino up to 360 GeV. These results, combined with searches in the single-lepton and all-jet final states, raise the exclusion limits up to 1050 GeV for the lightest top squark and up to 500 GeV for the lightest neutralino. For top squarks undergoing a cascade decay through charginos and sleptons, the mass limits reach up to 1300 GeV for top squarks and up to 800 GeV for the lightest neutralino. The results are also interpreted in a simplified model with a dark matter (DM) particle coupled to the top quark through a scalar or pseudoscalar mediator. For light DM, mediator masses up to 100 (50) GeV are excluded for scalar (pseudoscalar) mediators. The result for the scalar mediator achieves some of the most stringent limits to date in this model.
Highlights
The top quark couples to the Higgs boson more strongly than other fermions because of its large mass. It plays a prominent role in the so-called hierarchy problem [1,2] of the standard model (SM) of particle physics, since its dominant contribution in the loop corrections to the Higgs boson mass exposes the theory to higher energy scales present in nature
We present a search for top squark pair production in a final state with two leptons, hadronic jets identified as originating from b quarks, and significant transverse momentum imbalance
This model predicts the same final state as considered in SUSY phenomenology, with the transverse momentum imbalance provided by the dark matter (DM) particles
Summary
The top quark couples to the Higgs boson more strongly than other fermions because of its large mass. Assuming minimal flavor violation [34,35], the DM particles are dominantly produced in pairs in association with a tt pair (Fig. 1, lower right) This model predicts the same final state as considered in SUSY phenomenology, with the transverse momentum imbalance provided by the DM particles. Prior searches for such direct DM production via scalar and pseudoscalar mediators have been carried out at the LHC with 8 TeV data [36,37], and more recently with 13 TeV data [38,39,40]
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