Search for the weak decay $\psi (3686)\to {\mathrm{\Lambda }}_c^{+}{\bar{\mathrm{\Sigma }}}^{-}+c\mathrm{.}c$

Using $(448.1\pm 2.9)\times {10}^6$ $\psi (3686)$ events collected with the BESIII detector, we perform the first search for the weak baryonic decay $\psi (3686)\to {\mathrm{\Lambda }}_c^{+}{\bar{\mathrm{\Sigma }}}^{-}+c\mathrm{.}c\mathrm{.}$. The analysis procedure is optimized using a blinded method. No significant signal is observed, and the upper limit on the branching fraction ($\mathcal{B}$) of $\psi (3686)\to {\mathrm{\Lambda }}_c^{+}{\bar{\mathrm{\Sigma }}}^{-}+c\mathrm{.}c\mathrm{.}$ is set to be $1.4\times {10}^{-5}$ at the 90% confidence level.