Observation of the $\ddot{I}ˆ(1^3{D}_2)$ state in $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}{\hat{I}}^3\ddot{I}{‡}_{c1}$ at BESIII

Abstract

We report the observation of the $X(3823)$ in the process $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}X(3823)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}{\hat{I}}^3\ddot{I}{‡}_{c1}$ with a statistical significance of $6.2\ddot{I}ƒ$, in data samples at center-of-mass energies $\sqrt{s}=$4.230, 4.260, 4.360, 4.420 and 4.600~GeV collected with the BESIII detector at the BEPCII electron positron collider. The measured mass of the $X(3823)$ is $(3821.7\pm 1.3\pm 0.7)$~MeV/$c^2$, where the first error is statistical and the second systematic, and the width is less than $16$~MeV at the 90\% confidence level. The products of the Born cross sections for $e^{+}{e}^{-}\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}X(3823)$ and the branching ratio $\mathcal{B}[X(3823)\to {\hat{I}}^3\ddot{I}{‡}_{c1,c2}]$ are also measured. These measurements are in good agreement with the assignment of the $X(3823)$ as the $\ddot{I}ˆ(1^3{D}_2)$ charmonium state.

7 pages, 3 figures, version to appear in Phys. Rev. Lett