Measurement of $e^{+}{e}^{-}\to K\overline{K}J/\psi$ cross sections at center-of-mass energies from 4.189 to 4.600 GeV

We investigate the process $e^{+}{e}^{-}\to K\overline{K}J/\psi$ at center-of-mass energies from 4.189 to 4.600 GeV using $4.7{\mathrm{fb}}^{-1}$ of data collected by the BESIII detector at the BEPCII collider. The Born cross sections for the reactions $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ and $K_S^0{K}_S^{0}J/\psi$ are measured as a function of center-of-mass energy. The energy dependence of the cross section for $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ is shown to differ from that for ${\pi }^{+}{\pi }^{-}J/\psi$ in the region around the $Y(4260)$. In addition, there is evidence for a structure around 4.5 GeV in the $e^{+}{e}^{-}\to K^{+}{K}^{-}J/\psi$ cross section that is not present in ${\pi }^{+}{\pi }^{-}J/\psi$.

Figure 1

The distribution of lepton pair mass, $\mathrm{M}(l^{+}{l}^{-})$, for (a) ${\pi }^{+}{\pi }^{-}J/\psi$, (b) $K^{+}{K}^{-}J/\psi$, and (c) $K_S^0{K}_S^{0}J/\psi$. Data from all $E_{\mathrm{CM}}$ are combined. Points are for data; the green solid histograms are for signal MC events; and the red dashed histograms are for background MC events. The signal regions are shown by the gray dashed lines, while the sideband regions are shown with the blue dotted lines.

Figure 2

The invariant mass distributions for (a) $K^{\pm }J/\psi$ (two entries per event) and (b) $K^{+}{K}^{-}$. Data from all $E_{\mathrm{CM}}$ are combined. Black points are for data from the $J/\psi$ signal region; red points are for data from the $J/\psi$ sideband regions (normalized to the size of the signal region); dark green solid histograms are for signal MC events (normalized using the measured cross section at each $E_{\mathrm{CM}}$).

Figure 3

The Born cross sections (a) $\sigma ({\pi }^{+}{\pi }^{-}J/\psi )$, (b) $\sigma (K^{+}{K}^{-}J/\psi )$, and (c) $\sigma (K_S^0{K}_S^{0}J/\psi )$, and the ratios (d) $\sigma (K^{+}{K}^{-}J/\psi )/\sigma ({\pi }^{+}{\pi }^{-}J/\psi )$, and (e) $\sigma (K_S^0{K}_S^{0}J/\psi )/\sigma (K^{+}{K}^{-}J/\psi )$. The black points are for data sets with high integrated luminosities; the gray points are for smaller data sets. Thicker error bars are for statistical uncertainties only; thinner error bars are for combined statistical and systematic uncertainties. In (c), the large error bars with no central point are 90% C.L. upper limits. In (d), the inset shows a narrower region of $E_{\mathrm{CM}}$. The red dotted line in (e) is the value expected from isospin symmetry.