Based on electron-positron collision data collected with the BESIII detector operating at the Beijing Electron-Positron Collider II storage rings, the value of $R\equiv \sigma (e^{+}{e}^{-}\to \text{hadrons})/\sigma (e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-})$ is measured at 14 center-of-mass energies from 2.2324 to 3.6710 GeV. The resulting uncertainties are less than 3.0% and are dominated by systematic uncertainties.

A search for C P violation with an entangled system of Ξ − Ξ ¯ + pairs is performed, using ( 10 , 087 ± 44 ) × 10 6 J / ψ events collected with the BESIII experiment. A nine-dimensional helicity amplitude is used to fit e + e − → J / ψ → Ξ − Ξ ¯ + and its subsequent decays. The Ξ − and Ξ ¯ + decay parameters are determined with higher precision compared to the best results reported so far. Furthermore, the strong phase difference, ( δ P − δ S ) = ( 0.3 ± 1.2 ± 0.2 ) × 10 − 2 rad , and the weak phase difference, ( ξ P − ξ S ) = ( − 0.2 ± 1.2 ± 0.1 ) × 10 − 2 rad , are directly determined. These are the most precise measurements to date. The C P asymmetry observables A C P Ξ = ( − 7.8 ± 4.8 ± 0.8 ) × 10 − 3 and Δ ϕ C P Ξ = ( 0.6 ± 5.1 ± 0.2 ) × 10 − 3 rad are determined, which are consistent with C P conservation. In addition, independent measurements of the Λ decay parameter and C P asymmetry A C P Λ = ( − 2.9 ± 4.3 ± 0.7 ) × 10 − 3 are also obtained, which are in agreement with the previous measurements, but with much improved precision.

As the lightest charmed baryon, precision measurement of the pair production cross section of ${\Lambda }_c^{+}$ provides unprecedented experimental information for the investigation of baryon production mechanism. In addition, the extraction of the polar angle distributions of the outgoing ${\Lambda }_c^{+}$ in the annihilation of the electron–positron help to determine its electromagnetic form factors, which is currently the unique key to access the internal structure of the baryons. In this article, the measurement of $e^{+}{e}^{-}\to {\Lambda }_c^{+}{\overline{\Lambda }}_c^{-}$ process via the initial state radiation technique at Belle detector and direct electron–positron annihilation at BESIII with discrete center-of-mass energies near threshold are briefly reviewed. In addition, the electromagnetic form factor ratios of ${\Lambda }_c^{+}$ measured by BESIII are also investigated. A few theoretical models that parameterize the center-of-mass energy dependence of the cross section and electromagnetic form factors of baryon are introduced and the contributions of ${\Lambda }_c^{+}$ data to them are discussed.

A bstract: Using e ⁺ e ⁻ collision data corresponding to a total integrated luminosity of 20 fb ^{− 1} collected with the BESIII detector at the BEPCII collider, we present a measurement of the Born cross section for the process $$ {e}^{+}{e}^{-}\to p{K}^{-}{K}^{-}{\overline{\Xi}}^{+} $$ e + e − → p K − K − Ξ ¯ + at 39 center-of-mass energies between 3.5 and 4.9 GeV with a partial reconstruction technique. By performing a fit to the dressed cross section of $$ {e}^{+}{e}^{-}\to p{K}^{-}{K}^{-}{\overline{\Xi}}^{+} $$ e + e − → p K − K − Ξ ¯ + with a power law function for continuum production and one resonance at a time for the ψ (3770), ψ (4040), ψ (4160), ψ (4230), ψ (4360), ψ (4415) or ψ (4660), respectively, the upper limits for the product of partial electronic width and branching fraction into the final state $$ p{K}^{-}{K}^{-}{\overline{\Xi}}^{+} $$ p K − K − Ξ ¯ + for these resonances are determined at the 90% confidence level.

We report a direct search for a new gauge boson, X , with a mass of 17 MeV / c 2 , which could explain the anomalous excess of e + e − pairs observed in the Be 8 nuclear transitions. The search is conducted in the charmonium decays χ c J → X J / ψ ( J = 0 , 1 , 2 ) via the radiative transition ψ ( 3686 ) → γ χ c J using ( 2712.4 ± 14.3 ) × 10 6 ψ ( 3686 ) events collected with the BESIII detector at the BEPCII collider. No significant signal is observed, and the updated upper limit on the coupling strength of charm quark and the new gauge boson, ε c , is set to be | ε c | < 1.2 × 10 − 2 at 90% confidence level. We also report new constraints on the mixing strength ε between the Standard Model photon and dark photon γ ′ in the mass range from 5 to 300 MeV / c 2 . The upper limits at 90% confidence level vary within ( 2.5 – 17.5 ) × 10 − 3 depending on the γ ′ mass.