Study of the $ {\chi }_{cJ}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}{\eta }^{\prime }$ decays

Using a data sample of $ (2.712\pm 0.014)\times {10}^{9}\text{}\text{}\psi (3686)$ events collected with the BESIII detector at the BEPCII collider, we investigate the decays $ {\chi }_{cJ}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}{\eta }^{\prime }$ for $ J=0$, 1, 2 via the radiative transition $ \psi (3686)\to \gamma {\chi }_{cJ}$. The decays $ {\chi }_{c0,2}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}{\eta }^{\prime }$ are observed for the first time, with statistical significances of $ 6.7\sigma $ and $ 6.4\sigma $, respectively. Evidence for the decay $ {\chi }_{c1}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}{\eta }^{\prime }$ is found with a statistical significance of $ 3.3\sigma $. The corresponding branching fractions are measured to be $ ℬ({\chi }_{c0}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}{\eta }^{\prime })=\phantom{\rule{0ex}{0ex}}(7.56\pm 1.42\pm 0.90)\times {10}^{-5}$, $ ℬ({\chi }_{c1}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}{\eta }^{\prime })=(1.54\pm 0.51\pm 0.16)\times {10}^{-5}$, and $ ℬ({\chi }_{c2}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}{\eta }^{\prime })=\phantom{\rule{0ex}{0ex}}(3.03\pm 0.61\pm 0.29)\times {10}^{-5}$, where the first uncertainties are statistical and the second are systematic. No significant excited $ \mathrm{\Lambda }$ baryon states or $ \mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ near-threshold enhancements are observed.