Motivated by the experimental study of $J/��\to��~+$ invisible decay by the CLEO Collaboration, we analyze the process $J/��\to ����\bar��$, as the standard model background for this invisible decay, at the lowest order. Our investigation shows that Br($J/��\to ����\bar��$) is far below the present experimental upper limit on the branching ratio of $J/��\to��~+$ invisible, which indicates that some interesting room for new physics in this channel might be expected. We also present a similar analysis of the $��_c\to ����\bar��$ decay.

7 pages, 4 figures. An appendix added, published version