Probing a long-lived pseudoscalar in type-I 2HDM with displaced vertices and jets at the LHC

TL;DR

This work probes a long-lived pseudoscalar $A$ in the type-I 2HDM, where large $\tan\beta$ extends $A$'s lifetime and enables distinctive displaced-vertex signatures at the LHC. The authors study electroweak production of $A$ in association with $H$ or $H^{\pm}$ and subsequent decays $H^{\pm}/H\to W^{\pm}/Z A$, with $A\to b\bar{b}$, focusing on DV plus jets signatures in ATLAS/CMS inner detectors. They recast recent ATLAS DV+jets searches (original) and a modified, lower jet-$p_T$ threshold analysis, performing MC simulations and a detailed cutflow to derive $N_S$ and 95% CL sensitivities for Run-2 and the HL-LHC. The results indicate substantial portions of the $m_A$–$\tan\beta$ parameter space are already excluded by Run-2 data for $m_A>10$ GeV, while HL-LHC with the modified analysis can probe significantly broader regions, highlighting displaced-vertex channels as a powerful probe of LLPs in extended Higgs sectors.

Abstract

In the type-I two-Higgs-doublet model, the pseudoscalar $A$ can act as a long-lived particle (LLP) for sufficiently large values of $\tanβ$. At the LHC, the $A$ particles are predominantly produced in pairs through $pp \to W^*/Z^* \to H^\pm/H \, A$, with subsequent decays $H^{\pm}/H \to W^\pm/Z\, A$. The pseudoscalar $A$ typically decays into a pair of bottom quarks after traveling a macroscopic distance from its production point, giving rise to displaced-vertex (DV) signatures inside the inner detector. We perform Monte Carlo simulations of signal events with DVs plus jets, and assess the discovery prospects of $A$ as an LLP at the ATLAS and CMS experiments. Our findings show that a substantial portion of the parameter space with $m_A>10$ GeV has already been excluded by LHC Run-2 data, while the high-luminosity LHC will be able to probe broader regions.

Figures (9)

• Figure 1: All the points that satisfy the theoretical requirements and the oblique parameter bounds, for $10\text{ GeV}<m_A< 62.5\text{ GeV}$, shown in the $\tan\beta$ vs. $\cos{(\beta-\alpha)}$ plane (left) and the $\tan\beta$ vs. $R_f$ plane (right). Among them, the green and the red points are allowed and excluded by the joint constraints of Br$(h\to AA) < 0.107$ and the diphoton signal data of the 125 GeV Higgs, respectively.
• Figure 2: The same as figure \ref{['figxthe']}, but for $62.5\text{ GeV}<m_A<100\text{ GeV}$.
• Figure 3: All the points that satisfy the theoretical requirements, the oblique parameter bounds, Br$(h\to AA) < 0.107$, and the diphoton signal data of the 125 GeV Higgs, for $10\text{ GeV}<m_A< 100\text{ GeV}$.
• Figure 4: Left panel: Branching ratios of various decay channels of $A$. Right panel: The total decay width of $A$ vs. $m_A$ satisfying the constraints of theory and the oblique parameters, Br$(h\to AA) < 0.107$, and the diphoton signal data of the 125 GeV Higgs. The corresponding values of $c\tau_A$ are labeled on the right $y$-axis.
• Figure 5: The Feynman diagrams for the dominant production modes of $A$ via electroweak processes at the LHC.