The cross section for the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ is measured precisely at center-of-mass energies from 3.77 to 4.60 GeV using $9{\mathrm{fb}}^{-1}$ of data collected with the BESIII detector operating at the BEPCII storage ring. Two resonant structures are observed in a fit to the cross section. The first resonance has a mass of $(4222.0\pm 3.1\pm 1.4)\mathrm{MeV}/c^2$ and a width of $(44.1\pm 4.3\pm 2.0)\mathrm{MeV}$, while the second one has a mass of $(4320.0\pm 10.4\pm 7.0)\mathrm{MeV}/c^2$ and a width of $(101.4_{-19.7}^{+25.3}\pm 10.2)\mathrm{MeV}$, where the first errors are statistical and second ones are systematic. The first resonance agrees with the $Y(4260)$ resonance reported by previous experiments. The precision of its resonant parameters is improved significantly. The second resonance is observed in $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ for the first time. The statistical significance of this resonance is estimated to be larger than $7.6\sigma$. The mass and width of the second resonance agree with the $Y(4360)$ resonance reported by the BABAR and Belle experiments within errors. Finally, the $Y(4008)$ resonance previously observed by the Belle experiment is not confirmed in the description of the BESIII data.

The cross sections of $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{h}_c$ at center-of-mass energies from 3.896 to 4.600 GeV are measured using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The cross sections are found to be of the same order of magnitude as those of $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ and $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}\psi (2S)$, but the line shape is inconsistent with the $Y$ states observed in the latter two modes. Two structures are observed in the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{h}_c$ cross sections around 4.22 and $4.39\mathrm{GeV}/c^2$, which we call $Y(4220)$ and $Y(4390)$, respectively. A fit with a coherent sum of two Breit-Wigner functions results in a mass of $(4218.4_{-4.5}^{+5.5}\pm 0.9)\mathrm{MeV}/c^2$ and a width of $(66.0_{-8.3}^{+12.3}\pm 0.4)\mathrm{MeV}$ for the $Y(4220)$, and a mass of $(4391.5_{-6.8}^{+6.3}\pm 1.0)\mathrm{MeV}/c^2$ and a width of $(139.5_{-20.6}^{+16.2}\pm 0.6)\mathrm{MeV}$ for the $Y(4390)$, where the first uncertainties are statistical and the second ones systematic. The statistical significance of $Y(4220)$ and $Y(4390)$ is $10\sigma$ over one structure assumption.

The spin and parity of the $Z_c(3900{)}^{\pm }$ state are determined to be $J^P=1^{+}$ with a statistical significance larger than $7\sigma$ over other quantum numbers in a partial wave analysis of the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$. We use a data sample of $1.92{\mathrm{fb}}^{-1}$ accumulated at $\sqrt{s}=4.23$ and 4.26 GeV with the BESIII experiment. When parametrizing the $Z_c(3900{)}^{\pm }$ with a Flatté-like formula, we determine its pole mass $M_{\text{pole}}=(3881.2\pm 4.2_{\text{stat}}\pm 52.7_{\text{syst}})\mathrm{MeV}/c^2$ and pole width ${\mathrm{\Gamma }}_{\text{pole}}=(51.8\pm {4.6}_{\text{stat}}\pm {36.0}_{\text{syst}})\mathrm{MeV}$. We also measure cross sections for the process $e^{+}{e}^{-}\to Z_c(3900{)}^{+}{\pi }^{-}+\mathrm{c}.\mathrm{c}.\to J/\psi {\pi }^{+}{\pi }^{-}$ and determine an upper limit at the 90% confidence level for the process $e^{+}{e}^{-}\to Z_c(4020{)}^{+}{\pi }^{-}+\mathrm{c}.\mathrm{c}.\to J/\psi {\pi }^{+}{\pi }^{-}$.

The process $e^{+}{e}^{-}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ is studied using data samples at $\sqrt{s}=2.2324$, 2.400, 2.800 and 3.080 GeV collected with the BESIII detector operating at the BEPCII collider. The Born cross section is measured at $\sqrt{s}=2.2324\mathrm{GeV}$, which is 1.0 MeV above the $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ mass threshold, to be $305\pm 45_{-36}^{+66}\mathrm{pb}$, where the first uncertainty is statistical and the second systematic. The cross section near threshold is larger than that expected from theory, which predicts the cross section to vanish at threshold. The Born cross sections at $\sqrt{s}=2.400$, 2.800 and 3.080 GeV are measured and found to be consistent with previous experimental results, but with improved precision. Finally, the corresponding effective electromagnetic form factors of $\mathrm{\Lambda }$ are deduced.