A Review of Hyperon Physics at BESIII Experiment

TL;DR

This review surveys BESIII’s hyperon physics program enabled by the world's largest $J/\psi$ and $\psi(3686)$ samples, using angular-distribution and helicity-formalism techniques to extract hyperon polarization, CP-violating observables, and electromagnetic form factors in time-like regions. It details precise measurements of hyperon decay parameters, searches for CP violation, radiative and semileptonic decays, threshold and resonance-region cross sections, and novel hyperon–nucleon scattering studies using beam-pipe neutrons as targets. Key contributions include setting CP-violation limits at the $10^{-3}$ level, a three-order-magnitude improvement on the $\Lambda$ EDM, evidence for charmonium decays to hyperon pairs, and first measurements of elastic and inelastic Y–N scattering cross sections, constraining strong-interaction dynamics in the nonperturbative regime. The results advance our understanding of hyperon structure, weak interactions in the strange sector, and the role of hyperons in dense matter, with future upgrades and larger data samples poised to yield even more stringent tests of the Standard Model and insights into hadronic final states in $e^+e^-$ annihilation.

Abstract

The BESIII Collaboration has collected large data samples from $e^+e^-$ collisions at center-of-mass energies ranging from 1.84 to 4.95 GeV, which include the world's largest charmonium sample, consisting of 10 billion $J/ψ$ and 3 billion $ψ(3686)$ events. These high-statistics datasets enable BESIII to carry out a wide range of studies in hyperon physics. In this article, we review the major achievements of the BESIII Collaboration in this field, which can be broadly categorized into four areas: hyperon polarization and $CP$ violation, rare hyperon decays, hyperon pair production, and hyperon-nucleon interactions.

Figures (10)

• Figure S1: Orientation axes of the hyperon $H$ and antihyperon $\bar{H}$ helicity frames. $B$ represents the baryon produced by $H$ decay.
• Figure S2: Distributions of the polarization observables $\mu$ for $J/\psi \to \Lambda\bar{\Lambda}$BESIII:2022qax (a), $J/\psi/\psi(3686) \to \Sigma^0\bar{\Sigma}^0$BESIII:2024nif (c), and $J/\psi \to \Xi^0\bar{\Xi}^0$BESIII:2023drj (d); $M$ for $J/\psi/\psi(3686) \to \Sigma^+\bar{\Sigma}^-$BESIII:2025jxtBESIII:2023sgt (b); and $P_y$ for $J/\psi \to \Lambda\Sigma^0 + \text{c.c.}$BESIII:2023cvk (a), $\psi(3686) \to \Xi^0\bar{\Xi}^0$BESIII:2025dke (d), and $J/\psi/\psi(3686) \to \Xi^-\bar{\Xi}^+$BESIII:2021yprBESIII:2022lsz (e), as functions of $\cos\theta$ for each process. The dots with error bars represent the experimental data, the colored solid curves denote the global fit results, the dashed histograms correspond to the phase space (PHSP) Monte Carlo (MC) samples, and the red solid histograms show the PHSP MC weighted according to the global fit.
• Figure S3: Distribution of the test statistic $t=S^{J=1/2}-S^{J=3/2}$ (left), where the curves denote Gaussian fits to the simulated samples and the vertical bar marks the value of $t$ obtained from data. The dependence of the multipolar polarization operators on $\cos\theta_{\Omega^-}$ (right), where the solid lines represent the central values, and the shaded areas represent the range within one standard deviation BESIII:2020lkm.
• Figure S4: Distributions of the polarization observables $P_y$ for $e^+e^- \to \Lambda\bar{\Lambda}$ at $\sqrt{s} = 2.396$ GeV BESIII:2019nep (a) and $e^+e^- \to \Sigma^+\bar{\Sigma}^-$ at $\sqrt{s} = 2.396$–$2.900$ GeV BESIII:2023ynq (b,c), and $M$ for $e^+e^- \to \Lambda\bar{\Lambda}$ at $\sqrt{s} = 3.773$ GeV BESIII:2023euhBESIII:2025yzk (d,e) and $3.68$–$3.71$ GeV BESIII:2021cvv (f) and $e^+e^- \to \Sigma^+\bar{\Sigma}^-$ at $\sqrt{s} = 3.68$–$3.71$ GeV BESIII:2024dmr (g), as functions of $\cos\theta$ for each process. The dots with error bars represent the experimental data, the red curve shows the global fit, the gray and blue dashed histograms correspond to the PHSP MC, and the red polyline and colored solid histograms show the PHSP MC weighted according to the global fit.
• Figure S5: Distributions of $\alpha_{\gamma}$ versus branching fraction for $\Lambda \to n\gamma$BESIII:2022rgl (a), $\Sigma^+p\gamma$BESIII:2023fhs (b), and $\Xi^0\to\Lambda\gamma$BESIII:2024lio (c), along with the PDG values ParticleDataGroup:2024cfk and predictions from the vector meson dominance model (VDM) Zenczykowski:1991mx, pole model (PM I Gavela:1980bp and PM II Nardulli:1987ub), nonrelativistic constituent quark model (NRCQM) Niu:2020aoz, broken SU(3) model [BSU(3)] Zenczykowski:2005cs, and chiral perturbation theory (ChPT) Borasoy:1999ntShi:2022dhw.