Abstract
This paper presents a search for dark matter in the context of a two-Higgs-doublet model together with an additional pseudoscalar mediator, a, which decays into the dark-matter particles. Processes where the pseudoscalar mediator is produced in association with a single top quark in the 2HDM+a model are explored for the first time at the LHC. Several final states which include either one or two charged leptons (electrons or muons) and a significant amount of missing transverse momentum are considered. The analysis is based on proton–proton collision data collected with the ATLAS experiment at sqrt{s} = 13 TeV during LHC Run 2 (2015–2018), corresponding to an integrated luminosity of 139 hbox {fb}^{-1}. No significant excess above the Standard Model predictions is found. The results are expressed as 95% confidence-level limits on the parameters of the signal models considered.
Highlights
A class of simplified models for dark matter (DM) searches at the LHC is considered in this paper
This paper presents a dedicated search for single top quarks produced in association with DM candidates, exploiting final-state signatures characterised by the presence of: large ETmiss; jets, possibly arising from the fragmentation of bhadrons (b-jets); and one or two charged leptons, either electrons or muons ( = e, μ)
The largest background contribution in the tW1L and tj1L analysis channel SRs arises from ttproduction, whilst the contribution from ttV is largest in the tW2L SRs, with subdominant contributions from the tt, single-top and diboson processes
Summary
A class of simplified models for DM searches at the LHC is considered in this paper. It involves a two-Higgsdoublet extended sector together with an additional pseudoscalar mediator to DM, the 2HDM+a model [4,5]. [5], the masses of the heavy CP-even Higgs boson H and charged bosons H ± are set equal to the mass of the heavy CP-odd partner A This set of models offers a rich phenomenology, with a variety of final states that might arise depending on the production and decay modes of the various bosons composing the Higgs sector, as investigated in Ref. Previous searches for 2HDM+a models targeted associated production of DM candidates with Higgs or Z bosons [24], as well as DM and a ttpair (referred to as DMtt) The analysis is sensitive to DMttprocesses in regions of the parameter space where the DMt and DMttproduction rates are similar
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