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 $A\rightarrow HZ$ or $H\rightarrow AZ$, 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: $gg\rightarrow A/H\rightarrow HZ/AZ$, looking at final states bbll, \tau\tau ll and ZZZ(4l2j) for l =e,\mu. We further interpret these bounds in the context of the Type II Two Higgs Doublet Model, considering three different classes of processes: $A\rightarrow h^0Z$, $A\rightarrow H^0Z$, and $H^0 \rightarrow AZ$, in which $h^0$ and $H^0$ 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, $A\rightarrow h^0Z$ has the greatest reach when $H^0$ is interpreted as the 126 GeV Higgs: most regions in the tan\beta-sin(\beta-\alpha) parameter space can be covered by exclusion and discovery. For 126 GeV $h^0$, only relatively small tan\beta<10 (5) can be reached by exclusion (discovery). For $A\rightarrow H^0Z$, the reach is typically restricted to sin$(\beta-\alpha)\sim\pm 1$ with tan\beta <10 in bbll and \tau\tau ll channels. The ZZZ (4l2j) channel, on the other hand, covers a wide range of 0.3<|sin(\beta-\alpha)|<1 for tan\beta<4. $H^0\rightarrow AZ$ typically favors negative values of sin(\beta-\alpha), with exclusion/discovery reach possibly extending to all values of tan\beta. A study of exotic decays of extra Higgses would extend the reach at the LHC and provides nice complementarity to conventional Higgs search channels.
Highlights
Higgses into light Higgses, or Higgs plus gauge boson final states could be sizable
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
Assuming a discrete Z2 symmetry imposed on the Lagrangian, we are left with six free parameters, which can be chosen as four Higgs masses, the mixing angle α between the two CP-even Higgses, and the ratio of the two vacuum expectation values, 1Note that we use h0 and H0 to refer to the lighter or the heavier CP-even Higgs for models with two CP-even Higgs bosons
Summary
Searches for the non-SM like Higgses, mainly in the bb, μμ, τ τ or W W/ZZ channels have been performed both by ATLAS and CMS. In figure 1, we recast the current 95% C.L. limit of pp → Φ → τ +τ − in the (mA, tan β) parameter space of the Type II 2HDM [25] (left panel) and the projected 5σ reach at the 14 TeV LHC with 30 fb−1 luminosity [26] (right panel). In both plots, the solid black curves correspond to the limits in the MSSM, when mA ≈ mH0 with both A and H0 contributing to the signal. We analyze the process H → AZ for light A and its implication in the Type II 2HDM
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