Probing the decay $A^0\to h^0 Z^{(*)}$ in Two-Higgs-Doublet Models in the inverted hierarchy scenario at the Large Hadron Collider

TL;DR

This paper investigates the potential to detect the decay of a CP-odd scalar in Two-Higgs-Doublet Models at the LHC, focusing on the inverted hierarchy scenario and off-shell Z boson decays, proposing optimized selection strategies.

Contribution

It calculates the signal cross section for $A^0 o h^0 Z^{(*)}$ in 2HDMs under the inverted hierarchy scenario and suggests selection cuts for experimental sensitivity.

Findings

Large branching ratios for $A^0 o h^0 Z^*$ in 2HDMs, especially Type I.

No current limits for off-shell $Z^*$ decays in this context.

Proposed cuts could enhance detection sensitivity.

Abstract

Searches are being carried out at the Large Hadron Collider (LHC) for the decay of the CP-odd scalar ($A^0$) in Two-Higgs-Doublet Models (2HDMs) with Natural Flavour Conservation (NFC) in the channel $A^0\to h^0 Z$, where $h^0$ is either the discovered 125 GeV Higgs boson or is an undiscovered CP-even scalar with a mass below 125 GeV. The latter possibility is called the "inverted hierarchy scenario" (IH) and would provide the opportunity of simultaneous discovery of two scalars. In both searches the selection cuts are optimised for the case of an on-shell $Z$ boson. For the case of the $Z$ boson being off-shell (denoted by $Z^*$, for which $m_{A^0} - m_{h^0}<m_Z$) no limits are set on the relevant 2HDM parameters from this process. It is known that the decay $A^0\to h^0 Z^*$ can have a large branching ratio (BR) in 2HDMs (especially in the Type I structure). In the context of the IH scenario and developing our previous work, we calculate the signal cross section $\sigma(gg\to A^0)\times {\rm BR}(A^0\to h^0Z^{(*)})\times {\rm BR}(h^0\to b\overline b,\tau\overline \tau)$ in the four types of 2HDMs with NFC. We also suggest some selection cuts that could provide sensitivity to $A^0\to h^0 Z^*$ in the IH scenario.