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

We report on a study of the process e + e − → π ± ( D D ¯ * ) ∓ at s = 4.26 GeV using a 525 pb − 1 data sample collected with the BESIII detector at the BEPCII storage ring. A distinct charged structure is observed in the ( D D ¯ * ) ∓ invariant mass distribution. When fitted to a mass-dependent-width Breit-Wigner line shape, the pole mass and width are determined to be M pole = ( 3883 . 9 ± 1.5 ( stat ) ± 4.2 ( syst ) ) MeV / c 2 and Γ pole = ( 24 . 8 ± 3.3 ( stat ) ± 11 . 0 ( syst ) ) MeV . The mass and width of the structure, which we refer to as Z c ( 3885 ) , are 2 σ and 1 σ , respectively, below those of the Z c ( 3900 ) → π ± J / ψ peak observed by BESIII and Belle in π + π − J / ψ final states produced at the same center-of-mass energy. The angular distribution of the π 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 D ¯ * branching fraction of the Z c ( 3885 ) is measured to be σ ( e + e − → π ± Z c ( 3885 ) ∓ ) × B ( Z c ( 3885 ) ∓ → ( D D ¯ * ) ∓ ) = ( 83 . 5 ± 6.6 ( stat ) ± 22 . 0 ( syst ) ) pb . Assuming the Z c ( 3885 ) → D D ¯ * signal reported here and the Z c ( 3900 ) → π J / ψ signal are from the same source, the partial width ratio ( Γ ( Z c ( 3885 ) → D D ¯ * ) / Γ ( Z c ( 3900 ) → π J / ψ ) ) = 6.2 ± 1.1 ( stat ) ± 2.7 ( syst ) is determined.