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Analysis of $J/ψ(η_c)\to γ~+$ invisible decays in the standard model

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