Search for Invisible Decays of $η$ and $η^\prime$ in $J/ψ\to ϕη$ and $ϕη^\prime$

Abstract

Using a data sample of $58\times 10^6$ $J/ψ$ decays collected with the BES II detector at the BEPC, searches for invisible decays of $η$ and $η^\prime$ in $J/ψ$ to $ϕη$ and $ϕη^\prime$ are performed. The $ϕ$ signals, which are reconstructed in $K^+K^-$ final states, are used to tag the $η$ and $η^\prime$ decays. No signals are found for the invisible decays of either $η$ or $η^\prime$, and upper limits at the 90% confidence level are determined to be $1.65 \times 10^{-3}$ for the ratio $\frac{B(η\to \text{invisible})}{B(η\toγγ)}$ and $6.69\times 10^{-2}$ for $\frac{B(η^\prime\to \text{invisible})}{B(η^\prime\toγγ)}$. These are the first searches for $η$ and $η^\prime$ decays into invisible final states.