Measurement of the branching fraction for the decay $\psi \left(3686\right)\to \varphi {K}_{S}^{0}{K}_{S}^{0}$

Based on $\left(448.1±2.9\right)×{10}^{6}$ $\psi \left(3686\right)$ events collected with the BESIII detector operating at the BEPCII collider, the decay $\psi \left(3686\right)\to \varphi {K}_{S}^{0}{K}_{S}^{0}$ is observed for the first time. Taking the interference between $\psi \left(3686\right)$ decay and continuum production into account, the branching fraction of this decay is measured to be $B\left(\psi \left(3686\right)\to \varphi {K}_{S}^{0}{K}_{S}^{0}\right)=\left(3.53±0.20±0.21\right)×{10}^{-5}$, where the first uncertainty is statistical and the second is systematic. Combining with the world average value for $B\left(J/\psi \to \varphi {K}_{S}^{0}{K}_{S}^{0}\right)$, the ratio $B\left(\psi \left(3686\right)\to \varphi {K}_{S}^{0}{K}_{S}^{0}\right)/B\left(J/\psi \to \varphi {K}_{S}^{0}{K}_{S}^{0}\right)$ is determined to be $\left(6.0±1.6\right)%$, which is suppressed relative to the 12% rule.