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 $e^+e^-\to K^+K^-J/\psi$. A new resonance with a mass of $M = 4708_{ -15}^{ +17}\pm21$ MeV/$c^{ 2}$ and a width of $\Gamma = 126_{ -23}^{ +27}\pm30$ MeV is observed in the energy-dependent line shape of the $e^+e^-\to K^+K^-J/\psi$ cross section with a significance over $5\sigma$. The $K^{ +}J/\psi$ 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 $Z_{ cs}(3985)^{ \pm}/Z_{ cs}(4000)^{ \pm}\to K^{ \pm} J/\psi$ are reported at 90\% confidence levels. The ratio of branching fractions $\frac{ \mathcal{ B}(Z_{ cs}(3985)^{ +}\to K^+ J/\psi)}{ \mathcal{ B}(Z_{ cs}(3985)^{ +}\to (\bar{ D}^{ 0}D_s^{ *+} + \bar{ D}^{ *0}D_s^+))}$ is measured to be less than 0.03 at 90\% confidence level.
Categories: hep-ex