Using a sample of $1.31 \times 10^{ 9}$ $J/\psi$ events collected with the BESIII detector at the BEPCII collider, we study the decays of $J/\psi \rightarrow K_S K_L$ and $K_S K_S$. The branching fraction of$J/\psi\rightarrow K_S K_L$ is determined to be ${ \cal B}(J/\psi \rightarrow K_S K_L)=(1.93\pm0.01~(\rm{ stat.})\pm0.05~(\rm{ syst.}))\times10^{ -4}$, which significantly improves on previous measurements. No clear signal is observed for the $J/\psi \rightarrow K_S K_S$ process, and the upper limit at the 95% confidence level for its branching fraction is determined to be ${ \cal B}(J/\psi \rightarrow K_S K_S)<1.4\times10^{ -8}$, which improves on the previous searches by two orders in magnitude and reaches the order of the Einstein-Podolsky-Rosen expectation.
Categories: hep-ex