Analysis of $J/\psi ({\eta }_c)\to \gamma +$ invisible decays in the standard model

Abstract

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

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