Probing Type-I 2HDM light Higgs in the top-pair-associated diphoton channel

Abstract

Motivated by the possible 95 GeV diphoton excess, we investigate the capability of the Type-I Two-Higgs-Doublet Model (2HDM-I) to explain this signal under current theoretical and experimental constraints. Using full Monte Carlo (MC) simulations for the process of $pp \to t(\to W^+ b)\bar{t}(\to W^- \bar{b})h(\to γγ)$, we evaluate the discovery potential of a 95 GeV Higgs boson at future colliders. Direct Higgs searches strongly constrain the parameter $α$, excluding the region with $α\lesssim 0.95$. Monte Carlo results indicate that a minimum cross section of 0.3 fb is required to achieve a $5σ$ signal statistical significance at the HL-LHC with $L = 3~\mathrm{ab}^{-1}$. For the same luminosity, HE-LHC and FCC-hh require 0.67 fb and 2.36 fb, respectively. At the 14 TeV HL-LHC with an integrated luminosity of $3~\mathrm{ab}^{-1}$, parameter regions with $\sin(β-α) \gtrsim 0.4$ and $\sin(β-α) \gtrsim 0.25$ can be probed at the $5σ$ and $2σ$ significance levels, respectively. At the 27 TeV HE-LHC with $L = 10~\mathrm{ab}^{-1}$, the sensitivity improves to $\sin(β-α) \gtrsim 0.25$ ($5σ$) and $\gtrsim 0.15$ ($2σ$). For the 100 TeV FCC-hh with $L = 30~\mathrm{ab}^{-1}$, even regions with $\sin(β-α) \gtrsim 0.1$ or $\sin(β-α) \lesssim -0.05$ can be covered at the $5σ$ level. Parameter regions near $\sin(β-α) \approx 0$ remain challenging to probe in the diphoton channel, even with increased energy or luminosity.

Figures (6)

• Figure 1: Surviving samples in the $\tan\beta$ versus $\alpha$ (left) and $m_{12}$ versus $m_A$ planes (right) with colors indicating the branching ratio of $B\to X_s \gamma$ and the gray samples are excluded by Higgs direct search constraints.
• Figure 3: Surviving samples in the $\tan\beta$ versus $\alpha$ (left) and $m_{12}$ versus $m_A$ (right) planes. The color gradient in the upper panels represents the muon anomalous magnetic moment $\Delta a_{\mu}$, evaluated at the two-loop level. In the lower panels, blue plus signs (+), orange crosses ($\times$), and red stars (*) denote samples consistent with the WP25 results, the WP20 results, and both, respectively, within the $2\sigma$ range. Gray points correspond to samples that are incompatible with either result.
• Figure 4: Main Feynman Diagrams for the Process $pp \to t\bar{t}h(\to \gamma\gamma)$ at LO in 2HDM-I.
• Figure 5: Surviving samples on the $\tan\beta$ versus $\alpha$ plane, with colors indicating the cross section $\sigma(pp\to t\bar{t}h(\to \gamma\gamma))$ at 14 TeV High-Luminosity LHC (HL-LHC) (left), 27 TeV High-Energy LHC (HE-LHC) (middle), and 100 TeV Future Circular Collider (FCC-hh) (right).
• Figure 6: The normalized distributions of $\Delta R[j_1,\ j_2]$ (upper left), N$[j]$ (upper middle), $p_T^{j_1}$(upper right), $p_T^{l_1}$ (upper middle), $p_T^{\gamma_1}$(middle), $p_T^{\gamma_2}$ (middle right), $M_T [\gamma_1\gamma_2]$ (lower left), $M[\gamma_1\gamma_2]$ (lower middle) and $M[\gamma_1\gamma_2b]$ (lower right) for the signal and SM backgrounds at 14 TeV HL-LHC.