Observation of a Charged ${(D{\overline{D}}^{*})}^{\pm }$ Mass Peak in $e^{+}{e}^{-}\to \pi D{\overline{D}}^{*}$ at $\sqrt{s}=4.26\mathrm{GeV}$

We report on a study of the process $e^{+}{e}^{-}\to {\pi }^{\pm }{(D{\overline{D}}^{*})}^{\mp }$ at $\sqrt{s}=4.26\mathrm{GeV}$ using a $525\mathrm{pb}{}^{-1}$ data sample collected with the BESIII detector at the BEPCII storage ring. A distinct charged structure is observed in the ${(D{\overline{D}}^{*})}^{\mp }$ invariant mass distribution. When fitted to a mass-dependent-width Breit-Wigner line shape, the pole mass and width are determined to be $M_{\mathrm{pole}}=\mathbf{(}3883.9\pm 1.5(\mathrm{stat})\pm 4.2(\mathrm{syst})\mathbf{)}\mathrm{MeV}/c^2$ and ${\mathrm{\Gamma }}_{\mathrm{pole}}=\mathbf{(}24.8\pm 3.3(\mathrm{stat})\pm 11.0(\mathrm{syst})\mathbf{)}\mathrm{MeV}$. The mass and width of the structure, which we refer to as $Z_c(3885)$, are $2\sigma$ and $1\sigma$, respectively, below those of the $Z_c(3900)\to {\pi }^{\pm }J/\psi$ 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 $J^P=1^{+}$ quantum number assignment for the structure and disfavors $1^{-}$ or $0^{-}$. The Born cross section times the $D{\overline{D}}^{*}$ branching fraction of the $Z_c(3885)$ is measured to be ${\sigma \mathbf{(}{e}^{+}{e}^{-}\to {\pi }^{\pm }{Z}_c(3885)}^{\mp }\mathbf{)}\times {\mathcal{B}\mathbf{(}{Z}_c(3885)}^{\mp }\to {(D{\overline{D}}^{*})}^{\mp }\mathbf{)}=\mathbf{(}83.5\pm 6.6(\mathrm{stat})\pm 22.0(\mathrm{syst})\mathbf{)}\mathrm{pb}$. Assuming the $Z_c(3885)\to D{\overline{D}}^{*}$ signal reported here and the $Z_c(3900)\to \pi J/\psi$ signal are from the same source, the partial width ratio $(\mathrm{\Gamma }(Z_c(3885)\to D{\overline{D}}^{*})/\mathrm{\Gamma }(Z_c(3900)\to \pi J/\psi ))=6.2\pm 1.1(\mathrm{stat})\pm 2.7(\mathrm{syst})$ is determined.

Figure 1

The $\pi D$ recoil mass distribution for the (a) ${\pi }^{+}{D}^0$ and (b) ${\pi }^{-}{D}^{+}$ tag events. Points with errors are data, the hatched histogram shows the events from the $D$ mass sidebands. The solid and dashed histograms are described in the text.

Figure 2

The (a) $M(D^0{D}^{*-})$ and (b) $M(D^{+}{\overline{D}}^{*0})$ distributions for selected events. The curves are described in the text.

Figure 3

$(1/N_{\mathrm{tot}})dN/d|\cos {\theta }_{\pi }|\mathrm{versus}|\cos {\theta }_{\pi }|$ for $Z_c(3885)$ events in data. The solid, dashed, and dotted curves show expectations for $J^P=1^{+}$, $0^{-}$, and $1^{-}$, respectively.