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

We study the process $e^+e^- to (D^{*} bar{D}^{*})^{pm} pi^mp$ 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 $(137pm9pm15)$pb. We observe a structure near the $(D^{*} bar{D}^{*})^{pm}$ threshold in the $pi^mp$ recoil mass spectrum, which we denote as the $Z^{pm}_c(4025)$. The measured mass and width of the structure are $(4026.3pm2.6pm3.7)$MeV/c$^2$ and $(24.8pm5.6pm7.7)$MeV, respectively. Its production ratio $frac{sigma(e^+e^-to Z^{pm}_c(4025)pi^mp to (D^{*} bar{D}^{*})^{pm} pi^mp)}{sigma(e^+e^-to (D^{*} bar{D}^{*})^{pm} pi^mp)}$ is determined to be $0.65pm0.09pm0.06$. The first uncertainties are statistical and the second are systematic.