Observation of $\chi_{cJ}\to \Lambda\bar \Lambda \eta$

TL;DR

This paper reports the first observation of the decays of $oldsymbol{ ext{chi}_{cJ}}$ to $oldsymbol{ ext{Lambda}ar{ ext{Lambda}} ext{eta}}$ with significant statistical evidence, measuring their branching fractions using a large sample of $oldsymbol{ ext{psi}(3686)}$ events.

Contribution

First observation of $ ext{chi}_{cJ} o ext{Lambda}ar{ ext{Lambda}} ext{eta}$ decays with measured branching fractions, expanding understanding of charmonium decay modes.

Findings

Decays observed with significances of 13.9σ, 6.7σ, and 8.2σ for J=0, 1, 2.

Branching fractions measured as approximately 2.31×10⁻⁴, 5.86×10⁻⁵, and 1.05×10⁻⁴.

Large data sample of 448.1 million $ ext{psi}(3686)$ events used.

Abstract

By analyzing $(448.1\pm2.9)\times10^6$ $\psi(3686)$ events collected with the BESIII detector operating at the BEPCII collider, the decays of $\chi_{cJ} \to \Lambda\bar \Lambda \eta$ ($J=0$, 1 and 2) are observed for the first time with statistical significances of $13.9\sigma$, $6.7\sigma$, and $8.2\sigma$, respectively. The product branching fractions of $\psi(3686)\to\gamma\chi_{cJ}$ and $\chi_{cJ}\to \Lambda\bar \Lambda \eta$ are measured. Dividing by the world averages of the branching fractions of $\psi(3686)\to\gamma\chi_{cJ}$, the branching fractions of $\chi_{cJ}\to \Lambda\bar \Lambda \eta$ decays are determined to be $(2.31\pm0.30\pm0.21)\times10^{-4}$, $(5.86\pm1.38\pm0.68)\times10^{-5}$, and $(1.05\pm0.21\pm0.15)\times10^{-4}$ for $J=0$, 1 and 2, respectively, where the first uncertainties are statistical and the second systematic.