Constraints on a 2HDM with a singlet scalar and implications in the search for heavy bosons at the LHC

Abstract: We study a two-Higgs doublet model extended with an additional singlet scalar (2HDM+S), and provide a brief introduction to the model and its parameters. Constraints are applied to the parameter space of this model in order to accommodate a number of features in the data that have been interpreted in von Buddenbrock et al (2018 J. Phys. G 45 115003) as the result of the $H\rightarrow Sh$ decay produced via gluon-gluon fusion and in association with top quarks. Implications on the phenomenology of the heavy pseudo-scalar ($A$) and charged scalar ($H^+$) are discussed. In particular, the decays $A\rightarrow ZH$ and $H^+\rightarrow W^+H$ become prominent. This leads to final states with multiple leptons and $b$-quarks. The decay $A\rightarrow ZH\rightarrow ZSh$ results in the production of a high transverse momentum $Z$ produced in association with a lepton and two $b$-quarks with little additional jet activity. These predictions are compared to the data with model's benchmark points. With the parameters obtained here the model is able to accommodate the features at the LHC reported in von Buddenbrock et al (2018 J. Phys. G 45 115003). Without varying these parameters additional excesses in the $Zb\overline{b}$ and $t\overline{t}$ invariant mass spectra, and the production of $3$ leptons plus two $b$-tagged jets can be explained assuming $m_A\approx 600$\,GeV.