Exotic decays of a heavy neutral Higgs through HZ/AZ channel

Abstract: Models of electroweak symmetry breaking with extended Higgs sectors are theoretically well motivated. In this study, we focus on the Two Higgs Doublet Model with a low energy spectrum containing scalars H and a pseudoscalar A. We study the decays A → HZ or H → AZ, which could reach sizable branching fractions in certain parameter regions. With detailed collider analysis, we obtain model independent exclusion bounds as well as discovery reach at the 14 TeV LHC for the process: gg → A/H → HZ/AZ, looking at final states bbℓℓ, ττℓℓ and ZZZ(4ℓ + 2j) for ℓ = e, μ. We further interpret these bounds in the context of the Type II Two Higgs Doublet Model, considering three different classes of processes: A → h⁰Z, A → H⁰Z, and H⁰ → AZ, in which h⁰ and H⁰ are the light and heavy CP-even Higgses respectively. For 100 fb⁻¹ integrated luminosity at the 14 TeV LHC, we find that for parent particle mass around 300–400 GeV, A → h⁰Z has the greatest reach when H⁰ is interpreted as the 126 GeV Higgs: most regions in the tan β versus sin(β − α) plane can be excluded and a significant fraction at small and large tan β can be covered by discovery. For 126 GeV h⁰, only relatively small tan β ≲ 10 (5) can be reached by exclusion (discovery) while a wide range of sin(β − α) is accessible. For A → H⁰Z, the reach is typically restricted to sin(β − α) ~ ±1 with tan β ≲ 10 in bbℓℓ and ττℓℓ channels. The ZZZ(4ℓ2j) channel, on the other hand, covers a wide range of 0.3 < | sin(β − α)| < 1 for tan β ≲ 4. H⁰ → AZ typically favors negative values of sin(β − α), with exclusion/discovery reach possibly extending to all values of tan β. A study of exotic decays of extra Higgses appearing in extensions of the Standard Model would extend the reach at the LHC and provides nice complementarity to conventional Higgs search channels.