Search for Invisible Decays of $\eta$ and $\eta^\prime$ in $J/\psi \to \phi\eta$ and $\phi \eta^\prime$

TL;DR

This study searches for invisible decays of eta and eta' mesons in J/psi decays using BES II data, setting upper limits on their invisible decay rates, marking the first such search.

Contribution

First experimental search for invisible decays of eta and eta' mesons in J/psi decays, establishing upper limits on their decay rates.

Findings

No signals for invisible decays were observed.

Upper limits set at 90% confidence level for decay ratios.

First constraints on eta and eta' invisible decay modes.

Abstract

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