Dark matter production in association with a single top-quark at the LHC in a two-Higgs-doublet model with a pseudoscalar mediator

The sensitivity of the LHC experiments to the associated production of dark matter with a single top is studied in the framework of an extension of the standard model featuring two Higgs doublets and an additional pseudoscalar mediator. It is found that the experimental sensitivity is dominated by the on-shell production of a charged Higgs boson, when this assumes a mass below 1TeV. Dedicated selections considering one and two lepton final states are developed to assess the coverage in parameter space for this signature at a centre-of-mass energy of 14TeV assuming an integrated luminosity of 300 fb−1. For a pseudoscalar mediator, a, with mass 150GeV and maximally mixed with the pseudoscalar of the two Higgs doublets, all values of tanβ except for the range 3-15 can be excluded at 95% CL, if the H± mass is in the range 300GeV-1TeV. This novel signature complements the parameter space coverage of the mono-Higgs, mono-Z and tt̄+ETmiss signatures considered in previous publications for this model.