Searches for new physics beyond the Standard Model in hyperon sector

Abstract

Hyperon physics offers a distinctive laboratory for probing the intensity frontier and searching for physics beyond the Standard Model. This review summarizes recent results from the BESIII experiment, including pioneering studies of dark baryons, massless BSM particles, and invisible decay modes, together with investigations of baryon- and lepton-number violation. A central highlight is the determination of the $Λ$ electric dipole moment using quantum-entangled hyperon-antihyperon pairs, achieving a sensitivity three orders of magnitude beyond previous limits. These measurements provide world-leading constraints on new physics scenarios and establish a robust foundation for next-generation precision studies. By integrating experimental progress with theoretical developments and future facility prospects, this review emphasizes the critical role of hyperon probes in testing the fundamental laws of nature.

Figures (6)

• Figure 1: EDM effects visualization. The nominal fit, consistent with a null result within uncertainties, is shown by the black markers. In contrast, the red markers illustrate the expected distribution for a significant EDM of $|d_{\Lambda}| = 4.2 \times 10^{-18}\ e\text{ cm}$, manifesting as a $10\sigma$ departure from zero. The blue dashed line provides the theoretical baseline for a vanishing EDM.
• Figure 2: Constraints on the $s$-quark EDM $d_s$ and CEDM $\tilde{d}_s$ from the measurements on the $\Lambda$ and $n$ EDMs. (a) Scenario I: $d_s \gg d_u, d_d$ ; (b) Scenario II: $d_s=d_u=d_d$.
• Figure 3: The $E_{\text{EMC}}$ distribution for the $\Lambda \rightarrow \text{invisible}$ search. The dots with uncertainties represent data, while the solid line shows the $\Lambda \rightarrow n \pi^0$ background shape after data-driven corrections. The dashed line indicates the expected signal shape (normalized arbitrarily for clarity), which peaks near zero energy deposition.
• Figure 4: (a) Fitted $E_{\text{extra}}$ spectra for the process $\Sigma^+ \rightarrow p + \text{invisible}$; (b) Constraints at the $90\%$ C.L. on the effective axion--fermion decay constant associated with the $s \to d$ transition, as determined in this analysis. The shaded hatched area represents the region of parameter space excluded by the measurement. The quantities $F^{V}_{sd}$ and $F^{A}_{sd}$ correspond to the vector and axial-vector contributions to the decay constant, respectively.
• Figure 5: Summary of 95% C.L. constraints for $\Xi^- \to \pi^- + \text{invisible}$ under different $m_\chi$ assumptions: (a) upper limits on the branching fraction, and (b) the corresponding bounds on the Wilson coefficients $C_{us,s}^{L}$ and $C_{us,s}^{R}$, with LHC results shown for comparison.