Abstract
A search for dark matter produced in association with top quarks in proton-proton collisions at a center-of-mass energy of 13 TeV is presented. The data set used corresponds to an integrated luminosity of 35.9 fb−1 recorded with the CMS detector at the LHC. Whereas previous searches for neutral scalar or pseudoscalar mediators considered dark matter production in association with a top quark pair only, this analysis also includes production modes with a single top quark. The results are derived from the combination of multiple selection categories that are defined to target either the single top quark or the top quark pair signature. No significant deviations with respect to the standard model predictions are observed. The results are interpreted in the context of a simplified model in which a scalar or pseudoscalar mediator particle couples to a top quark and subsequently decays into dark matter particles. Scalar and pseudoscalar mediator particles with masses below 290 and 300 GeV, respectively, are excluded at 95% confidence level, assuming a dark matter particle mass of 1 GeV and mediator couplings to fermions and dark matter particles equal to unity.
Highlights
Dirac fermions, the interaction Lagrangian terms for the production of a scalar (φ) or pseudoscalar (a) mediator particle can be expressed as: Lφ
The underlying simplified models explored in these results, unlike the one presented in eqs. (1.1) and (1.2), assume either the resonant production of a +2/3 charged and colored spin-0 boson that decays into a right-handed top quark and one dark matter (DM) particle, or a spin-1 mediator with flavor changing neutral current interactions
Considering these models, in addition to the DM particle, only one top quark is assumed to be produced in the final state, unlike the t/t+DM processes considered in this search where the top quark is produced through SM-like diagrams alongside a light quark or a W boson
Summary
Events in the SL channel are required to contain ≥1 identified b-tagged jet, at least 2 jets with pT > 30 GeV, and pmTiss > 160 GeV. After the mT selection, the remaining tt background is primarily from events where both top quarks decay leptonically (tt(2 )) and one lepton is not identified This background can be further reduced by making use of the mW T2 variable [54], which is defined as the minimal value of the mass of a particle assumed to be pair produced and to decay to a W boson and a b quark jet. The tt background is further reduced by requiring that the transverse mass mbT of the pTmiss vector and of a b-tagged jet is greater than 180 GeV, where mbT is defined to eq (4.1) but considering a b-tagged jet instead of a lepton. Each region is identified by a unique name, where 0 denotes exactly zero leptons, 1(2) b-tag represents exactly 1 (at least 2) b-tagged jet, and 0 FJ or 1 FJ denotes exactly zero or at least one forward jet
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
