The search for dark matter candidate, ALP, together with CP-odd Higgs boson and tau leptons at $\sqrt{s}=14$ TeV

Technical Summary of arXiv:2401.02528v1

Problem Statement
Cosmological observations, including gravitational lensing, cosmic microwave background data, and galactic rotation speeds, confirm that approximately 27% of the Universe consists of dark matter. While the nature of these particles remains unknown, Beyond the Standard Model (BSM) theories—such as superstrings and D-branes—predict candidates like WIMPs, dilatons, and axions. Among these, the Axion-Like Particle (ALP) is a prominent candidate. However, identifying ALPs is complicated by the lack of precise information regarding their mass, scalar or pseudoscalar nature, and the fact that their interaction is primarily gravitational. This ambiguity creates significant challenges for both experimental identification and theoretical interpretation.

Methodology
To address these challenges, the authors employed the Two-Higgs-Doublet Model plus a pseudoscalar mediator (2HDM+a) as a reference framework. This model introduces 12 additional parameters with specific constraints:

• The masses of the CP-odd ($A$), CP-even ($H$), and charged ($H^\pm$) Higgs bosons are set to be equal.
• The mixing angles $\alpha$ and $\beta$ are constrained such that $\cos(\beta - \alpha) = 0$.
• The lightest Higgs boson mass is fixed at $m_h \approx 125$ GeV.
• The mixing angle between the two pseudoscalars, $\theta$, is set to satisfy either $\sin \theta = 0.35$ or $\sin \theta = 0.7$.

The study utilized the MadGraph5_aMC@NLO program to simulate the production of the CP-odd Higgs boson ($A$) at a center-of-mass energy of $\sqrt{s} = 14$ TeV. The specific process investigated is $pp \to A \to ah\tau^+\tau^-$, where the CP-odd boson decays into an ALP ($a$) and the lightest Higgs boson ($h$), with the Higgs subsequently decaying into tau leptons.

The simulation scenarios were guided by experimental constraints from the ATLAS collaboration (based on 139 fb$^{-1}$ of data at $\sqrt{s} = 13$ TeV). Two specific parameter sets (BP1 and BP2) were selected for analysis:

• BP1: $m_a = 500$ GeV, $m_A = 1400$ GeV, $\tan \beta = 1$, $\sin \theta = 0.35$.
• BP2: $m_a = 150$ GeV, $m_A = 500$ GeV, $\tan \beta = 2$, $\sin \theta = 0.7$.

Key Results
The authors calculated the production cross-sections for the Higgs boson ($A$) and the axion ($a$) as functions of their respective masses. Furthermore, they analyzed the kinematic distributions of the final state particles:

• Transverse Momentum ($p_T$): The data indicates a predominance of momentum values for the CP-odd Higgs boson ($A$) in the 400–600 GeV range. For the ALP, the momentum values are predominantly found in the 100–400 GeV range.
• Pseudorapidity ($\eta$): For the CP-odd Higgs boson, events are concentrated in the region from $-3$ to $3$. For the ALP, the pseudorapidity distribution is more symmetrical, particularly in the BP2 scenario, where events cluster between $-1.5$ and $1.5$.

Significance and Claims
The paper claims that the derived kinematic constraints on transverse momentum and angular distributions provide a basis for targeted searches for BSM physics. Specifically, the results suggest the feasibility of searching for a CP-odd Higgs boson with a mass around 400 GeV and an ALP dark matter candidate with a mass up to 200 GeV.

The authors modestly conclude that the BP2 scenario demonstrates priority over BP1, noting that it correlates more closely with the latest experimental constraints established by the ATLAS collaboration. The work serves to model optimal mass regions and kinematic restrictions to facilitate the identification of ALPs and associated Higgs bosons in future high-energy collisions.