Constraining $A\to ZH$ with $H\to t\bar t$ in the Low-Mass Region

Saiyad Ashanujjaman; Guglielmo Coloretti; Andreas Crivellin; Siddharth P. Maharathy; Bruce Mellado

doi:10.1103/9jdj-hg8y

paper

Constraining $A \to Z H$ with $H \to t t ˉ$ in the Low-Mass Region

arXiv:2510.23714 · doi:10.1103/9jdj-hg8y

Abstract

The decay $A \to Z H$ is a characteristic signal of two-Higgs-doublet models (2HDMs), where $A$ and $H$ lie primarily within the same $S U (2)_{L}$ multiplet, leading to a coupling of order $g_{2}$ to the $Z$ boson. The subsequent decay $H \to t t^{(*)}$ is particularly promising, as it gives rise to distinct final states involving multiple leptons and $b$ -jets. The required splitting between $m_{A}$ and $m_{H}$ can naturally occur near the electroweak scale while being consistent with perturbative unitarity. Whereas dedicated ATLAS and CMS searches focused on the region with both top-quarks on-shell, we cover lower masses where one top quark is off-shell by recasting Standard Model $t t ˉ Z$ measurements of ATLAS and CMS. The obtained limits on $σ (A \to Z H) \times Br (H \to t t ˉ)$ are between $0.12$ pb and $0.62$ pb. Interestingly, we observe these stringent limits despite a preference (up to $2.5 σ$ ) for a non-zero new physics signal, most pronounced around for $m_{A} \approx 450 - 460$ GeV and $m_{H} \approx 290$ GeV, with a best-fit value of $σ (A \to Z H) \times Br (H \to t t ˉ) \approx 0.3$ pb. This cross section can be accommodated within a top-philic 2HDM for a top-Yukawa coupling of the second Higgs doublet of $μ_{t} ≳ 0.16$ .

arXiv commentVersion to appear in Phys. Rev. D (as a Letter)

Constraining A→ZH with H→ttˉ in the Low-Mass Region

Abstract

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Constraining $A \to Z H$ with $H \to t t ˉ$ in the Low-Mass Region