Observation of a Neutral Structure near the $D{\bar{D}}^{\ast }$ Mass Threshold in $e^{+}{e}^{-}\to (D{\bar{D}}^{\ast }{)}^0\ddot{I}{€}^0$ at $\sqrt{s}$ = 4.226 and 4.257 GeV

Abstract

A neutral structure in the $D{\bar{D}}^{\ast }$ system around the $D{\bar{D}}^{\ast }$ mass threshold is observed with a statistical significance greater than 10$\ddot{I}ƒ$ in the processes $e^{+}{e}^{-}\to D^{+}{D}^{\ast -}\ddot{I}{€}^0+c.c.$ and $e^{+}{e}^{-}\to D^0{\bar{D}}^{\ast 0}\ddot{I}{€}^0+c.c.$ at $\sqrt{s}$ = 4.226 and 4.257 GeV in the BESIII experiment. The structure is denoted as $Z_c(3885{)}^0$. Assuming the presence of a resonance, its pole mass and width are determined to be ($3885.7_{-5.7}^{+4.3}$(stat)$\pm 8.4$(syst)) MeV/$c^2$ and ($35_{-12}^{+11}$(stat)$\pm 15$(syst)) MeV, respectively. The Born cross sections are measured to be $\ddot{I}ƒ(e^{+}{e}^{-}\to Z_c(3885{)}^0\ddot{I}{€}^0,Z_c(3885{)}^0\to D{\bar{D}}^{\ast })=(77\pm 13$(stat)$\pm 17$(syst)) pb at 4.226 GeV and ($47\pm 9$(stat)$\pm 10$(syst)) pb at 4.257 GeV. The ratio of decay rates $\frac{\mathcal{B}(Z_c(3885{)}^0\to D^{+}{D}^{\ast -}+c.c.)}{\mathcal{B}(Z_c(3885{)}^0\to D^0{\bar{D}}^{\ast 0}+c.c.)}$ is determined to be $0.96\pm 0.18$(stat)$\pm 0.12$(syst), consistent with no isospin violation in the process $Z_c(3885{)}^0\to D{\bar{D}}^{\ast }$.

7 pages, 2 figures