Observation of a vector charmoniumlike state at 4.7 $\mathrm{GeV}/c^2$ and search for $Z_{cs}$ in $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\ddot{I}ˆ$

Abstract

Using data samples with an integrated luminosity of 5.85~fb${}^{-1}$ collected at center-of-mass energies from 4.61 to 4.95 GeV with the BESIII detector operating at the BEPCII storage ring, we measure the cross section for the process $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\ddot{I}ˆ$. A new resonance with a mass of $M=4708_{-15}^{+17}\pm 21$ MeV/$c^2$ and a width of $\hat{I}“=126_{-23}^{+27}\pm 30$ MeV is observed in the energy-dependent line shape of the $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\ddot{I}ˆ$ cross section with a significance over $5\ddot{I}ƒ$. The $K^{+}J/\ddot{I}ˆ$ system is also investigated to search for charged charmoniumlike states, but no significant $Z_{cs}^{+}$ states are observed. Upper limits on the Born cross sections for $e^{+}{e}^{-}\to K^{-}{Z}_{cs}(3985{)}^{+}/K^{-}{Z}_{cs}(4000{)}^{+}+c.c.$ with $Z_{cs}(3985{)}^{\pm }/Z_{cs}(4000{)}^{\pm }\to K^{\pm }J/\ddot{I}ˆ$ are reported at 90\% confidence levels. The ratio of branching fractions $\frac{\mathcal{B}(Z_{cs}(3985{)}^{+}\to K^{+}J/\ddot{I}ˆ)}{\mathcal{B}(Z_{cs}(3985{)}^{+}\to ({\bar{D}}^0{D}_s^{\ast +}+{\bar{D}}^{\ast 0}{D}_s^{+}))}$ is measured to be less than 0.03 at 90\% confidence level.