Charged Higgs-boson pair production in association with the $Z^0$ boson at electron-positron colliders

TL;DR

This paper analyzes the production of charged Higgs pairs with a Z boson at electron-positron colliders within the two-Higgs-doublet model, exploring cross sections, decay channels, and the impact of beam polarization for future detection.

Contribution

It provides a detailed tree-level calculation of the process in 2HDM, considering experimental constraints, various scenarios, and polarization effects, which advances understanding of charged Higgs production at colliders.

Findings

Cross section up to 0.278 fb for m_H±=175 GeV in Type-I

Cross section down to 0.073 fb for m_H±=500 GeV in Type-II

Beam polarization enhances cross section by up to 2.5 times

Abstract

In this paper, the production of the charged Higgs pair associated with the $Z^0$ boson is analyzed in the minimal extension of the standard model the so-called two-Higgs-doublet model (2HDM). The process $e^+e^- \rightarrow H^+H^-Z^0$ is calculated at the tree level including all the possible diagrams in 2HDM. The numerical analysis is performed in consideration of the current experimental constraints and various scenarios for the free parameters of the model. The results are presented as a function of center-of-mass energy, the charged Higgs mass ($m_{H^\pm}$), and the ratio of the vacuum expectation values ($t_\beta$). The unpolarized cross section, taking into account the results in the flavor physics, gets up to $0.278\text{ fb}$ for $m_{H^\pm}=175\text{ GeV}$, and it declines with decreasing $m_{H^\pm}$ in Type-I. However, it gets down to $0.073\text{ fb}$ for $m_{H^\pm}=500\text{ GeV}$ in Type-II. Further, the calculation is also carried out in the non-alignment scenario and low-$m_{h^0}$ scenario. The effect of the polarized incoming $e^+$ and $e^-$ beams shows that the cross section is enhanced by a factor up to 2.5 at P(+0.60,-0.80) polarization configuration. Decay channels of the charged Higgs, possible final states of the process, and some differential distributions belong to the charged Higgs and $Z^0$ boson are examined for each scenario. The analysis shows that some channels have higher branching ratio such as $H^+\rightarrow t \bar{b}$, $H^+\rightarrow W^+h^0$, and $H^+\rightarrow W^+H^0$. These decay channels are essential for the charged Higgs searches in the lepton colliders regarding the scenarios interested. The detection of the charged Higgs is a powerful sign for the extended scalar sectors, and the results show the potential of a future lepton collider.