Measurement of the branching fraction of $ \psi (3686)$ $ \to \omega \eta \eta $

Using a sample of ($ 2.712\pm 0.014$)$ \times {10}^{9}\text{}\text{}\psi (3686)$ events collected with the BESIII detector at the BEPCII collider in 2009, 2012, and 2021, the decay $ \psi (3686)\to \omega \eta \eta $ is observed for the first time. The branching fraction of the $ \psi (3686)\to \omega \eta \eta $ decay is measured to be ($ 1.65\pm 0.02\pm 0.21$)$ \times {10}^{-5}$, where the first uncertainty is statistical and the second systematic.