[Paper Review] Constraints on the axial-vector and pseudo-scalar mediated WIMP-nucleus interactions from PandaX-4T experiment

Zhou Huang, Chencheng Han+89 more|arXiv (Cornell University)|Aug 7, 2022

Dark Matter and Cosmic Phenomena4 citations

TL;DR

This paper presents the most stringent constraints to date on spin-dependent WIMP-nucleus interactions from the PandaX-4T experiment, using 1.6 ton·years of commissioning data. It sets a 90% C.L. upper limit of $5.8 \times 10^{-42}$ cm² on the WIMP-neutron cross section at 40 GeV/$c^2$, with improved sensitivity over ATLAS in the few-hundred GeV WIMP mass range, using both tree-level and loop-level contributions in a 2HDM+a model framework.

ABSTRACT

We present the constraints on the axial-vector and pseudo-scalar mediated WIMP-nucleus interactions from the PandaX-4T experiment, using the data set corresponding to a total exposure of 0.63~tonne$\cdot$year. No significant signal excess is observed, and the most stringent upper limits to date on the spin-dependent WIMP-neutron scattering cross section are set at 90\% confidence level with the minimum WIMP-neutron scattering cross section of 5.8$ imes 10^{-42}$\si{\cm^{2}} for WIMP mass of 40~\si{\GeV/}$c^2$. Exclusion limits on the axial-vector and pseudo-scalar simplified models are also derived.

Motivation & Objective

• To establish the most stringent experimental limits on spin-dependent WIMP-nucleus interactions using direct detection data.
• To probe the parameter space of the 2HDM+a model, particularly for WIMP masses above several hundred GeV/c².
• To complement collider constraints (e.g., ATLAS, CMS) in the high-mass WIMP regime by leveraging the high-sensitivity underground detector.
• To evaluate the impact of loop-induced contributions (axial-vector and pseudo-scalar mediated) on WIMP-nucleon scattering cross sections.
• To provide normalized exclusion limits relative to theoretical model predictions, enabling direct comparison with collider and astrophysical constraints.

Proposed method

• The analysis uses 1.6 ton·years of commissioning data from the PandaX-4T experiment, collected in the China Jinping Underground Laboratory.
• Background models and statistical inference techniques are identical to those used in the PandaX-4T spin-independent analysis, ensuring consistency and robustness.
• The theoretical framework employs a two-Higgs-doublet model with an additional singlet scalar (2HDM+a), including both tree-level and loop-level contributions to the WIMP-nucleus scattering amplitude.
• The scattering cross section is calculated using the formula $\sigma^{\rm SI}_{\chi N} = \frac{\mu^{2}_{N}|C^{\rm loop}_{N}|^{2}}{\pi}$, with loop coefficients $C^{\rm loop}_{N}$ depending on 11 model parameters.
• A set of conventional parameter values is adopted: $\tan\beta = 10$, $m_h = 125$ GeV, $m_H = m_{H^\pm} = m_A = 600$ GeV, $m_a = 250$ GeV, $\theta = 0.1$, $c_1 = 0$, $c_2 = 1$, $g_\chi = 1$.
• Exclusion limits are computed at 95% C.L. and normalized to the theoretical cross section ($\sigma_{\rm theory}$) to enable comparison with collider results.

Experimental results

Research questions

• RQ1 What are the most stringent limits on spin-dependent WIMP-neutron and WIMP-proton scattering cross sections from the PandaX-4T experiment?
• RQ2 How does the sensitivity of PandaX-4T compare to collider constraints (e.g., ATLAS) in the high-mass WIMP regime (>300 GeV/c²)?
• RQ3 To what extent do loop-induced axial-vector and pseudo-scalar mediated interactions contribute to the WIMP-nucleus scattering cross section in the 2HDM+a model?
• RQ4 What is the normalized exclusion limit (ratio of excluded to theoretical cross section) as a function of WIMP mass in the 2HDM+a model?
• RQ5 How do the results from PandaX-4T complement and constrain the parameter space of simplified dark matter models beyond the reach of colliders?

Key findings

• The PandaX-4T experiment sets the most stringent 90% C.L. upper limit on the WIMP-neutron spin-dependent cross section at $5.8 \times 10^{-42}$ cm², achieved at a WIMP mass of 40 GeV/$c^2$.
• The 90% C.L. upper limit on the WIMP-proton spin-dependent cross section is $1.7 \times 10^{-40}$ cm², also at 40 GeV/$c^2$.
• For the 2HDM+a model, the PandaX-4T 95% C.L. normalized exclusion limit (ratio of excluded to theoretical cross section) improves upon ATLAS constraints for WIMP masses above several hundred GeV/$c^2$.
• The experiment demonstrates enhanced sensitivity to loop-mediated WIMP-nucleus interactions, particularly in the high-mass region where collider searches are less effective.
• The results are consistent with the theoretical model under the adopted parameter set, with the relic density curve (from ATLAS) overlaid for reference, showing compatibility with cosmological constraints.
• The analysis confirms the viability of direct detection experiments in probing the high-mass WIMP region, especially when combined with collider and astrophysical data.