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A bstract With data samples collected with the BESIII detector at seven energy points at s = 3 . 68 − 3 . 71 GeV, corresponding to an integrated luminosity of 333 pb − 1 , we present a study of the Λ transverse polarization in the e + e − → Λ Λ ¯ reaction. The significance of polarization by combining the seven energy points is found to be 2.6 σ including the systematic uncertainty, which implies a non-zero phase between the transition amplitudes of the Λ Λ ¯ helicity states. The modulus ratio and the relative phase of EM- psionic form factors combined with all energy points are measured to be R Ψ = 0.71 − 0.10 + 0.10 ± 0.03 and ∆Φ Ψ = 23 − 8.0 + 8.8 ± 1.6 ° , where the first uncertainties are statistical and the second systematic.

Using e + e − collision data corresponding to a total integrated luminosity of 12.9 fb − 1 collected with the BESIII detector at the BEPCII collider, the exclusive Born cross sections and the effective form factors of the reaction$$ {e}^{+}{e}^{-}\\to {\\Xi}^{-}{\\overline{\\Xi}}^{+} $$e + e − → Ξ − Ξ ¯ + are measured via the single baryon-tag method at 23 center-of-mass energies between 3.510 and 4.843 GeV. Evidence for the decay$$ \\psi (3770)\\to {\\Xi}^{-}{\\overline{\\Xi}}^{+} $$ψ 3770 → Ξ − Ξ ¯ + is observed with a significance of 4.5 σ by analyzing the measured cross sections together with earlier BESIII results. For the other charmonium(-like) states ψ (4040), ψ (4160), Y (4230), Y (4360), ψ (4415), and Y (4660), no significant signal of their decay to$$ {\\Xi}^{-}{\\overline{\\Xi}}^{+} $$Ξ − Ξ ¯ + is found. For these states, upper limits of the products of the branching fraction and the electronic partial width at the 90% confidence level are provided.

A bstract Using e + e − collision data collected by the BESIII detector at BEPCII corresponding to an integrated luminosity of 30 fb − 1 , we measure Born cross sections and effective form factors for the process e + e − → Ξ 0 Ξ ¯ 0 at forty-five center-of-mass energies between 3.51 and 4.95 GeV. The dressed cross section is fitted, assuming a power-law function plus a charmonium(-like) state, i.e., ψ (3770), ψ (4040), ψ (4160), ψ (4230), ψ (4360), ψ (4415) or ψ (4660). No significant charmonium(-like) state decaying into Ξ 0 Ξ ¯ 0 is observed. Upper limits at the 90% confidence level on the product of the branching fraction and the electronic partial width are provided for each decay. In addition, ratios of the Born cross sections and the effective form factors for e + e − → Ξ 0 Ξ ¯ 0 and e + e − → Ξ − Ξ ¯ + are also presented to test isospin symmetry and the vector meson dominance model.

A bstract Based on (1 . 0087 ± 0 . 0044) × 10 10 J/ψ events collected with the BESIII detector at the BEPCII e + e − storage ring, we search for K S 0 invisible decays via the J/ψ → ϕ K S 0 K S 0 process. No significant signal is observed, and the upper limit of the branching fraction of these invisible decays is set at 8.4 × 10 − 4 at the 90% confidence level. This is the first experimental search for K S 0 invisible decays.

A bstract Based on a sample of (2712 . 4 ± 14 . 3) × 10 6 ψ (3686) events collected with the BESIII detector, a partial wave analysis of the decay ψ 3686 → Λ Σ ¯ 0 π 0 + c . c . is performed to investigate Λ * and Σ * resonances in the π 0 Σ ¯ 0 and π 0 Λ invariant mass distributions. Significant contributions are found from the Λ(1405), Λ(1520), Λ(1600), Λ(1670), Λ(1690), Λ(1800), Λ(1890), Λ(2325), Σ(1385), Σ(1660), Σ(1670), Σ(1750), and Σ(1910). The masses, widths, and production branching fractions for each component are determined. In addition, the branching fraction of ψ 3686 → Λ Σ ¯ 0 π 0 + c . c . is measured to be (1 . 544 ± 0 . 013 ± 0 . 071) × 10 − 4 for the first time, where the first uncertainty is statistical and the second systematic.

Using e + e − collision data at 13 center-of-mass energies ranging from 4.600 to 4.951 GeV collected with the BESIII detector, we conduct the first search for the e + e − →$$ {K}_S^0{K}_S^0{h}_c $$K S 0 K S 0 h c process and investigate the resonance structures in the cross section line shape. No significant signal is observed, and the upper limits of the Born cross sections at each center-of-mass energy are presented. The ratio$$ \\frac{\\sigma \\left({e}^{+}{e}^{-}\\to {K}_S^0{K}_S^0{h}_c\\right)}{\\sigma \\left({e}^{+}{e}^{-}\\to {K}_S^0{K}_S^0J/\\psi \\right)} $$σ e + e − → K S 0 K S 0 h c σ e + e − → K S 0 K S 0 J / ψ is determined to be 0.15 ± 0.22. This result indicates that if vector states exist in this energy region, their decay into h c is significantly suppressed compared to decays into J / ψ .

Based on (1 . 0087 ± 0 . 0044) × 10 10 J/ψ events collected with the BESIII detector at the BEPCII e + e − storage ring, we search for$$ {K}_S^0 $$K S 0 invisible decays via the J/ψ →$$ \\phi {K}_S^0{K}_S^0 $$ϕ K S 0 K S 0 process. No significant signal is observed, and the upper limit of the branching fraction of these invisible decays is set at 8.4 × 10 − 4 at the 90% confidence level. This is the first experimental search for$$ {K}_S^0 $$K S 0 invisible decays.

Based on (2712 . 4 ± 14 . 3) × 10 6 ψ (3686) events collected at the BESIII detector operating at the BEPCII collider, we present the first observation of the decay$$ \\psi (3686)\\to {K}^{-}\\Lambda (1520){\\overline{\\Xi}}^{+} $$ψ 3686 → K − Λ 1520 Ξ ¯ + + c.c.. The product branching fraction$$ \\mathcal{B}\\left[\\psi (3686)\\to {K}^{-}\\Lambda (1520){\\overline{\\Xi}}^{+}+\\textrm{c}.\\textrm{c}.\\right]\\times \\mathcal{B}\\left[\\Lambda (1520)\\to p{K}^{-}\\right] $$B ψ 3686 → K − Λ 1520 Ξ ¯ + + c . c . × B Λ 1520 → p K − is measured to be (9 . 47 ± 0 . 75 ± 0 . 97) × 10 − 7 , where the first uncertainty is statistical and the second systematic.

A bstract Based on (2712 . 4 ± 14 . 3) × 10 6 ψ (3686) events collected at the BESIII detector operating at the BEPCII collider, we present the first observation of the decay ψ 3686 → K − Λ 1520 Ξ ¯ + + c.c.. The product branching fraction B ψ 3686 → K − Λ 1520 Ξ ¯ + + c . c . × B Λ 1520 → p K − is measured to be (9 . 47 ± 0 . 75 ± 0 . 97) × 10 − 7 , where the first uncertainty is statistical and the second systematic.

The process$$ {e}^{+}{e}^{-}\\to {K}_S^0{K}_S^0\\psi (3686) $$e + e − → K S 0 K S 0 ψ 3686 is studied by analyzing e + e − collision data samples collected at eight center-of-mass energies ranging from 4.682 to 4.951 GeV with the BESIII detector operating at the BEPCII collider, corresponding to an integrated luminosity of 4 . 1 fb − 1 . Observation of the$$ {e}^{+}{e}^{-}\\to {K}_S^0{K}_S^0\\psi (3686) $$e + e − → K S 0 K S 0 ψ 3686 process is found for the first time with a statistical significance of 6 . 3 σ , and the cross sections at each center-of-mass energy are measured. The ratio of cross sections of$$ {e}^{+}{e}^{-}\\to {K}_S^0{K}_S^0\\psi (3686) $$e + e − → K S 0 K S 0 ψ 3686 relative to e + e − → K + K − ψ (3686) is determined to be$$ \\frac{\\sigma \\left({e}^{+}{e}^{-}\\to {K}_S^0{K}_S^0\\psi (3686)\\right)}{\\sigma \\left({e}^{+}{e}^{-}\\to {K}^{+}{K}^{-}\\psi (3686)\\right)}=0.45\\pm 0.25 $$σ e + e − → K S 0 K S 0 ψ 3686 σ e + e − → K + K − ψ 3686 = 0.45 ± 0.25 , which is consistent with the prediction based on isospin symmetry. The uncertainty includes both statistical and systematic contributions. Additionally, the$$ {K}_S^0\\psi (3686) $$K S 0 ψ 3686 invariant mass distribution is found to be consistent with three-body phase space. The significance of a contribution beyond three-body phase space is only 0 . 8 σ .