Charged Higgs boson production in association with a top quark in MC@NLO

TL;DR

The paper develops a next-to-leading-order QCD calculation of charged Higgs production in association with a top quark within the MC@NLO framework, enabling accurate, exclusive predictions when matched to parton showers. It treats two mass regimes: m_H > m_t, where the process is well-defined, and m_H < m_t, where interference with top-pair production necessitates Diagram Removal or Diagram Subtraction definitions to separate single-top from top-pair contributions. The authors implement and validate both Catani–Seymour and FKS subtraction schemes, study interference effects, and examine threshold behavior, providing practical MC@NLO configurations and cuts (e.g., a p_t veto) to control interference at the LHC. The work enhances the precision modeling of H±t production, essential for charged-Higgs searches and for disentangling scalar sector dynamics in extensions of the Standard Model.

Abstract

We discuss the calculation of charged Higgs boson production in association with top quark in the MC@NLO framework for combining NLO matrix elements with a parton shower. The process is defined in a model independent manner for wide applicability, and can be used if the charged Higgs boson mass is either greater or less than the mass of the top quark. For the latter mass region, care is needed in defining the charged Higgs production mode due to interference with top pair production. We give a suitable definition applicable in an NLO (plus parton shower) context, and present example results for the LHC.

Figures (7)

• Figure 1: Leading order diagrams for single top production (double line) in association with a charged Higgs boson (dashed line).
• Figure 2: Subset of NLO real emission contributions to $H^-t$ production, consisting of top pair production with decay of the antitop quark to produce a charged Higgs boson and $\bar{b}$ quark.
• Figure 3: Comparison of NLO and MC@NLO results, with parameters as given in the text. Shown are the transverse momentum and rapidity distributions of the top quark (upper line) and Higgs boson (middle line), the transverse momentum of the $H^-t$ system (bottom left) and the azimuthal angle between the top quark and charged Higgs boson (bottom right).
• Figure 4: Normalized transverse momentum distributions of the two hardest jets. We include the detector cuts of eq. (\ref{['eq:detector']}). First row: the two hardest $b$ jets; second row: the two hardest light-flavor jets for a leptonic top decay; third row: the two hardest light-flavor jets for a hadronic top decay. The left-hand column corresponds to ${ m_{H^-}} =300$ GeV, and the right-hand column to ${ m_{H^-}} =800$ GeV.
• Figure 5: Normalized rapidity distributions of the two hardest jets. We include the detector cuts of eq. (\ref{['eq:detector']}). First row: the two hardest $b$ jets; second row: the two hardest light-flavor jets for a leptonic top decay; third row: the two hardest light-flavor jets for a hadronic top decay. The left-hand column corresponds to ${ m_{H^-}} =300$ GeV, and the right-hand column to ${ m_{H^-}} =800$ GeV.