Observation of a neutral charmoniumlike state $Z_c(4025{)}^0$ in $e^{+}{e}^{-}\to (D^{\ast }{\bar{D}}^{\ast }{)}^0\ddot{I}{€}^0$

Abstract

We report a study of the process $e^{+}{e}^{-}\to (D^{\ast }{\bar{D}}^{\ast }{)}^0\ddot{I}{€}^0$ using $e^{+}{e}^{-}$ collision data samples with integrated luminosities of $1092{\mathrm{pb}}^{-1}$ at $\sqrt{s}=4.23\mathrm{GeV}$ and $826{\mathrm{pb}}^{-1}$ at $\sqrt{s}=4.26\mathrm{GeV}$ collected with the BESIII detector at the BEPCII storage ring. We observe a new neutral structure near the $(D^{\ast }{\bar{D}}^{\ast }{)}^0$ mass threshold in the $\ddot{I}{€}^0$ recoil mass spectrum, which we denote as $Z_c(4025{)}^0$. Assuming a Breit-Wigner line shape, its pole mass and pole width are determined to be $(4025.5_{-4.7}^{+2.0}\pm 3.1)\mathrm{MeV}/{\mathrm{c}}^2$ and $(23.0\pm 6.0\pm 1.0)\mathrm{MeV}$, respectively. The Born cross sections of $e^{+}{e}^{-}\to Z_c(4025{)}^0\ddot{I}{€}^0\to (D^{\ast }{\bar{D}}^{\ast }{)}^0\ddot{I}{€}^0$ are measured to be $(61.6\pm 8.2\pm 9.0)\mathrm{pb}$ at $\sqrt{s}=4.23\mathrm{GeV}$ and $(43.4\pm 8.0\pm 5.4)\mathrm{pb}$ at $\sqrt{s}=4.26\mathrm{GeV}$. The first uncertainties are statistical and the second are systematic.

7 pages, 2 figures and 1 table