Observation of a Charged Charmoniumlike Structure in e⁺e⁻ → (D*D̅*)^± π^∓ at √s=4.26 GeV

We study the process e⁺e⁻ → (DD̅)^± π^∓ at a center-of-mass energy of 4.26 GeV using a 827 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 ± 9 ± 15) pb. We observe a structure near the (DD̅)^± threshold in the π^∓ recoil mass spectrum, which we denote as the Z_c ^±(4025). The measured mass and width of the structure are (4026.3 ± 2.6 ± 3.7) MeV/c² and (24.8 ± 5.6 ± 7.7) MeV, respectively. Its production ratio σ(e⁺ e⁻ → Z_c ^±(4025)π^∓ → (DD̅)^± π^∓ / σ(e⁺ e⁻ → ((DD̅)^± π^∓ is determined to be 0.65 ± 0.09 ± 0.06. The first uncertainties are statistical and the second are systematic.