Observation of $\chi_{c2}\to\eta'\eta'$ and $\chi_{c0,2}\to\eta\eta'$

TL;DR

This paper reports the first observation of certain $ ext{chi}_c$ decays into $ ext{eta}$ and $ ext{eta'}$ mesons, providing precise measurements of their branching fractions and insights into decay mechanisms.

Contribution

First observation of $ ext{chi}_c2 o ext{eta'} ext{eta'}$, $ ext{chi}_c0 o ext{eta} ext{eta'}$, and $ ext{chi}_c2 o ext{eta} ext{eta'}$ decays with improved measurement precision.

Findings

First observation of the decays with high statistical significance.

Precise branching fraction measurements for the observed decays.

Clarification of decay mechanisms involving OZI-disconnected amplitudes.

Abstract

Using a sample of $447.9\times 10^6$ $\psi(3686)$ events collected with the BESIII detector in 2009 and 2012, we study the decays $\chi_{c0,2}\to$ $\eta'\eta'$ and $\eta\eta'$. The decays $\chi_{c2}\to\eta'\eta'$, $\chi_{c0}\to\eta\eta'$ and $\chi_{c2}\to\eta\eta'$ are observed for the first time with statistical significances of $9.6\sigma$, $13.4\sigma$ and $7.5\sigma$, respectively. The branching fractions are determined to be $\mathcal{B}(\chi_{c0}\to\eta'\eta') =(2.19\pm0.03\pm0.14)\times10^{-3}$, $\mathcal{B}(\chi_{c2}\to\eta'\eta') = (4.76\pm0.56\pm0.38)\times10^{-5}$, $\mathcal{B}(\chi_{c0}\to\eta\eta') = (8.92\pm0.84\pm0.65)\times10^{-5}$ and $\mathcal{B}(\chi_{c2}\to\eta\eta') = (2.27\pm0.43\pm0.25)\times10^{-5}$, where the first uncertainties are statistical and the second systematic. The precision for the measurement of $\mathcal{B}(\chi_{c0}\to\eta'\eta')$ is significantly improved compared to previous measurements. Based on the measured branching fractions, the role played by the doubly and singly Okubo-Zweig-Iizuka disconnected transition amplitudes for $\chi_{c0,2}$ decays into pseudoscalar meson pairs can be clarified.