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

TL;DR

This paper investigates the potential of the LHC to detect dark matter produced alongside a single top-quark within a two-Higgs-doublet model featuring a pseudoscalar mediator, focusing on charged Higgs production.

Contribution

It introduces a new search strategy for dark matter in association with a single top-quark in a two-Higgs-doublet model with a pseudoscalar mediator, emphasizing charged Higgs production.

Findings

Charged Higgs production dominates sensitivity for masses below 1 TeV.

Parameter space with tanβ between 3 and 15 can be excluded at 95% CL.

The signature complements existing dark matter search channels.

Abstract

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 1 TeV. 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 14 TeV assuming an integrated luminosity of 300 fb$^{-1}$. For a pseudoscalar mediator with mass 150 GeV and maximally mixed with the pseudoscalar of the two Higgs doublets, values of $tan\beta$ up to 3 and down to 15 can be excluded at 95% CL, if the $H^{\pm}$ mass is in the range 300 GeV-1 TeV. This novel signature complements the parameter space coverage of the mono-Higgs, mono-Z and $t{\bar t}$+$E_{\mathrm T}^{\mathrm miss}$ signatures considered in previous publications for this model.