Observation and branching fraction measurements of $J\mathrm{/}\psi \to p\bar{p}{K}_S^0{K}_S^0$ and $\psi (3686)\to p\bar{p}{K}_S^0{K}_S^0$

Using $(10.087\pm 0.044)\times {10}^9$ $J\mathrm{/}\psi$ events and $(2.712\pm 0.014)\times {10}^9$ $\psi (3686)$ events collected by the BESIII detector operating at the BEPCII collider, we report the first observation of the hadronic decays of $J\mathrm{/}\psi \to p\bar{p}{K}_S^0{K}_S^0$ and $\psi (3686)\to p\bar{p}{K}_S^0{K}_S^0$, both with statistical significance greater than $10\sigma$. Their branching fractions are determined to be $\mathcal{B}(J\mathrm{/}\psi \to p\bar{p}{K}_S^0{K}_S^0)=(1.60\pm 0.02\pm 0.09)\times {10}^{-5}$ and $\mathcal{B}(\psi (3686)\to p\bar{p}{K}_S^0{K}_S^0)=(3.93\pm 0.24\pm 0.34)\times {10}^{-6}$. The ratio of their branching fractions is $\mathcal{B}(\psi (3686)\to p\bar{p}{K}_S^0{K}_S^0)\mathrm{/}\mathcal{B}(J\mathrm{/}\psi \to p\bar{p}{K}_S^0{K}_S^0)=(24.6\pm 1.5\pm 2.1)\mathrm{\%}$, which deviates from theoretical expectation by 4.6$\sigma$. Here the first uncertainties are statistical and the second systematic. We have also examined the $p\bar{p}$ invariant mass distributions in these decays, and no significant enhancement around the $p\bar{p}$ near threshold is found.