Precision measurement of the branching fraction of \boldmath $J\mathrm{/}\psi \to K^{+}{K}^{-}$ via $\psi (2S)\to {\pi }^{+}{\pi }^{-}J\mathrm{/}\psi$

Using a sample of $448.1\times {10}^6$ $\psi (2S)$ events collected with the BESIII detector, we perform a study of the decay $J\mathrm{/}\psi \to K^{+}{K}^{-}$ via $\psi (2S)\to {\pi }^{+}{\pi }^{-}J\mathrm{/}\psi$. The branching fraction of $J\mathrm{/}\psi \to K^{+}{K}^{-}$ is determined to be ${\mathcal{B}}_{K^{+}{K}^{-}}=(3.072\pm 0.023(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}\mathrm{.})\pm 0.050(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}\mathrm{.}))\times {10}^{-4}$, which is consistent with previous measurements but with significantly improved precision.