Observation of $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}ˆ(3770)$ and $D_1(2420{)}^0{\bar{D}}^0+c.c.$

Abstract

Several intermediate states of the reaction channels $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}{D}^0{\bar{D}}^0$ and $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}{D}^{+}{D}^{-}$ are studied using the data samples collected with the BESIII detector at center-of-mass energies above 4.08 GeV. For the first time in this final state, a $\ddot{I}ˆ(3770)$ signal is seen in the $D\bar{D}$ invariant mass spectrum, with a statistical significance of $5.2\ddot{I}ƒ$ at $\sqrt{s}=4.42$ GeV. There is also evidence for this resonance at $\sqrt{s}$ = 4.26 and 4.36 GeV with statistical significance of 3.2$\ddot{I}ƒ$ and 3.3$\ddot{I}ƒ$, respectively. In addition, the Born cross section of $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}\ddot{I}ˆ(3770)$ is measured. The proposed heavy-quark-spin-symmetry partner of the $X(3872)$, the state $X_2(4013)$, is also searched for in the $D\bar{D}$ invariant mass spectra. No obvious signal is found. The upper limit of the Born cross section of the process $e^{+}{e}^{-}\to \ddot{I}{}^0{X}_2(4013)$ combined with the branching fraction is measured. Also, the processes $e^{+}{e}^{-}\to D_1(2420)\bar{D}+c.c.$ are investigated. The neutral mode with $D_1(2420{)}^0\to D^0\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ is reported with statistical significance of 7.4$\ddot{I}ƒ$ at $\sqrt{s}=4.42$ GeV for the first time, and evidence with statistical significance of 3.2$\ddot{I}ƒ$ and 3.3$\ddot{I}ƒ$ at $\sqrt{s}$ = 4.36 and 4.60 GeV is seen, respectively. No evident signal for the process $e^{+}{e}^{-}\to D_1(2420{)}^0{\bar{D}}^0+c.c.,D_1(2420{)}^0\to D^{\ast +}\ddot{I}{€}^{-}$ is reported. Evidence for $e^{+}{e}^{-}\to D_1(2420{)}^{+}{D}^{-}+c.c.,D_1(2420{)}^{+}\to D^{+}\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ is reported with statistical significance of 3.1$\ddot{I}ƒ$ and 3.0$\ddot{I}ƒ$ at $\sqrt{s}$ = 4.36 and 4.42 GeV, respectively.