We study the process $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ at a center-of-mass energy of 4.260 GeV using a $525{\mathrm{pb}}^{-1}$ data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross section is measured to be $(62.9\pm 1.9\pm 3.7)\mathrm{pb}$, consistent with the production of the $Y(4260)$. We observe a structure at around $3.9\mathrm{GeV}/c^2$ in the ${\pi }^{\pm }J/\psi$ mass spectrum, which we refer to as the $Z_c(3900)$. If interpreted as a new particle, it is unusual in that it carries an electric charge and couples to charmonium. A fit to the ${\pi }^{\pm }J/\psi$ invariant mass spectrum, neglecting interference, results in a mass of $(3899.0\pm 3.6\pm 4.9)\mathrm{MeV}/c^2$ and a width of $(46\pm 10\pm 20)\mathrm{MeV}$. Its production ratio is measured to be $R=(\sigma \mathbf{(}{e}^{+}{e}^{-}\to {\pi }^{\pm }{Z}_c(3900{)}^{\mp }\to {\pi }^{+}{\pi }^{-}J/\psi \mathbf{)}/\sigma (e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi ))=(21.5\pm 3.3\pm 7.5)\%$. In all measurements the first errors are statistical and the second are systematic.

We study $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}{h}_c$ at center-of-mass energies from 3.90 to 4.42 GeV by using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The Born cross sections are measured at 13 energies and are found to be of the same order of magnitude as those of $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J/\psi$ but with a different line shape. In the ${\pi }^{\pm }{h}_c$ mass spectrum, a distinct structure, referred to as $Z_c(4020)$, is observed at $4.02\mathrm{GeV}/c^2$. The $Z_c(4020)$ carries an electric charge and couples to charmonium. A fit to the ${\pi }^{\pm }{h}_c$ invariant mass spectrum, neglecting possible interferences, results in a mass of $(4022.9\pm 0.8\pm 2.7)\mathrm{MeV}/c^2$ and a width of $(7.9\pm 2.7\pm 2.6)\mathrm{MeV}$ for the $Z_c(4020)$, where the first errors are statistical and the second systematic. The difference between the parameters of this structure and the $Z_c(4025)$ observed in the $D^{*}{\overline{D}}^{*}$ final state is within $1.5\sigma$, but whether they are the same state needs further investigation. No significant $Z_c(3900)$ signal is observed, and upper limits on the $Z_c(3900)$ production cross sections in ${\pi }^{\pm }{h}_c$ at center-of-mass energies of 4.23 and 4.26 GeV are set.

We report on a study of the process $e^{+}{e}^{-}\to {\pi }^{\pm }{(D{\overline{D}}^{*})}^{\mp }$ at $\sqrt{s}=4.26\mathrm{GeV}$ using a $525\mathrm{pb}{}^{-1}$ data sample collected with the BESIII detector at the BEPCII storage ring. A distinct charged structure is observed in the ${(D{\overline{D}}^{*})}^{\mp }$ invariant mass distribution. When fitted to a mass-dependent-width Breit-Wigner line shape, the pole mass and width are determined to be $M_{\mathrm{pole}}=\mathbf{(}3883.9\pm 1.5(\mathrm{stat})\pm 4.2(\mathrm{syst})\mathbf{)}\mathrm{MeV}/c^2$ and ${\mathrm{\Gamma }}_{\mathrm{pole}}=\mathbf{(}24.8\pm 3.3(\mathrm{stat})\pm 11.0(\mathrm{syst})\mathbf{)}\mathrm{MeV}$. The mass and width of the structure, which we refer to as $Z_c(3885)$, are $2\sigma$ and $1\sigma$, respectively, below those of the $Z_c(3900)\to {\pi }^{\pm }J/\psi$ peak observed by BESIII and Belle in ${\pi }^{+}{\pi }^{-}J/\psi$ final states produced at the same center-of-mass energy. The angular distribution of the $\pi Z_c(3885)$ system favors a $J^P=1^{+}$ quantum number assignment for the structure and disfavors $1^{-}$ or $0^{-}$. The Born cross section times the $D{\overline{D}}^{*}$ branching fraction of the $Z_c(3885)$ is measured to be ${\sigma \mathbf{(}{e}^{+}{e}^{-}\to {\pi }^{\pm }{Z}_c(3885)}^{\mp }\mathbf{)}\times {\mathcal{B}\mathbf{(}{Z}_c(3885)}^{\mp }\to {(D{\overline{D}}^{*})}^{\mp }\mathbf{)}=\mathbf{(}83.5\pm 6.6(\mathrm{stat})\pm 22.0(\mathrm{syst})\mathbf{)}\mathrm{pb}$. Assuming the $Z_c(3885)\to D{\overline{D}}^{*}$ signal reported here and the $Z_c(3900)\to \pi J/\psi$ signal are from the same source, the partial width ratio $(\mathrm{\Gamma }(Z_c(3885)\to D{\overline{D}}^{*})/\mathrm{\Gamma }(Z_c(3900)\to \pi J/\psi ))=6.2\pm 1.1(\mathrm{stat})\pm 2.7(\mathrm{syst})$ is determined.

We study the process $e^{+}{e}^{-}\to (D^{*}{\overline{D}}^{*}{)}^{\pm }{\pi }^{\mp }$ at a center-of-mass energy of 4.26 GeV using a $827{\mathrm{pb}}^{-1}$ data sample obtained with the BESIII detector at the Beijing Electron Positron Collider. Based on a partial reconstruction technique, the Born cross section is measured to be $(137\pm 9\pm 15)\mathrm{pb}$. We observe a structure near the $(D^{*}{\overline{D}}^{*}{)}^{\pm }$ threshold in the ${\pi }^{\mp }$ recoil mass spectrum, which we denote as the $Z_c^{\pm }(4025)$. The measured mass and width of the structure are $(4026.3\pm 2.6\pm 3.7)\mathrm{MeV}/{\mathrm{c}}^2$ and $(24.8\pm 5.6\pm 7.7)\mathrm{MeV}$, respectively. Its production ratio $\sigma (e^{+}{e}^{-}\to Z_c^{\pm }(4025){\pi }^{\mp }\to (D^{*}{\overline{D}}^{*}{)}^{\pm }{\pi }^{\mp })/\sigma (e^{+}{e}^{-}\to (D^{*}{\overline{D}}^{*}{)}^{\pm }{\pi }^{\mp })$ is determined to be $0.65\pm 0.09\pm 0.06$. The first uncertainties are statistical and the second are systematic.

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.