Observation of a charged (DD*bar)- mass peak in e+e- --> pi+ (DD*bar)- at Ecm=4.26 GeV

Abstract: We report on a study of the process e+e- --> pi+(D D*bar)- at Ecm=4.26 GeV using a 525 /pb data sample collected with the BESIII detector at the BEPCII storage ring. A distinct charged structure is observed in the (DD*bar)- invariant mass distribution. When fitted to a mass-dependent-width Breit-Wigner lineshape, the pole mass and width are determined to be M_pole=(3883.9 +- 1.5 +- 4.2) MeV and Gamma_pole=(24.8 +- 3.3 +- 11.0) MeV. The mass and width of the structure, which we refer to as Z_c(3885), are 2sigma and 1sigma, respectively, below those of the Z_c(3900) --> pi+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 JP=1+ quantum number assignment for the structure and disfavors 1- or 0-. The Born cross section times the DD*bar branching fraction of the Z_(3885) is measured to be sigma(e+e- --> pi+ Z_c(3885)-) x Bf(Z_c(3885)-->DD*bar)=(83.5 +-6.6 +- 22.0) pb. Assuming the Z_c(3885) --> DD*bar signal reported here and the Z_c(3900) --> pi J/psi signal are from the same source, the partial width ratio Gamma(Z_c(3885) --> DD*bar)/Gamma(Z_c(3900) -->pi J/psi)=6.2 +- 1.1 +- 2.7 is determined.