Observation of a charged charmoniumlike structure in $e^{+}{e}^{-}\to (D^{\ast }{\bar{D}}^{\ast }{)}^{\pm }{\pi }^{\mp }$ at $\sqrt{s}=4.26$GeV

We study the process $e^{+}{e}^{-}\to (D^{\ast }{\bar{D}}^{\ast }{)}^{\pm }{\pi }^{\mp }$ at a center-of-mass energy of 4.26GeV using a 827pb${}^{-1}$ 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 $(137\pm 9\pm 15)$pb. We observe a structure near the $(D^{\ast }{\bar{D}}^{\ast }{)}^{\pm }$ 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 $(4026.3\pm 2.6\pm 3.7)$MeV/c${}^2$ and $(24.8\pm 5.6\pm 7.7)$MeV, respectively. Its production ratio $\frac{\sigma(e^+e^-\to Z^{\pm}_c(4025)\pi^\mp \to (D^{} \bar{D}^{})^{\pm} \pi^\mp)}{\sigma(e^+e^-\to (D^{} \bar{D}^{})^{\pm} \pi^\mp)}$isdeterminedtobe$0.65\pm0.09\pm0.06$. The first uncertainties are statistical and the second are systematic.