Precision Studies and Searches for CP Asymmetries in the Inclusive Decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }X$

Based on $e^{+}{e}^{-}$ annihilation data collected with the BESIII detector at center-of-mass energies from 4.600 to 4.699 GeV, corresponding to an integrated luminosity of 4.5 fb${}^{-1}$, we present the first measurement of the longitudinal polarization of $\mathrm{\Lambda }$ hyperons produced in the inclusive decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }X$, where $X$ denotes any allowed final state. The polarizations are determined to be ${\mathcal{P}}_{\mathrm{\Lambda }}=-0.393\pm {0.055}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{.}}\pm {0.020}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{.}}$ and ${\mathcal{P}}_{\bar{\mathrm{\Lambda }}}=0.288\pm {0.056}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{.}}\pm {0.017}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{.}}$. We then search for CP violation using an asymmetry constructed from the $\mathrm{\Lambda }$ polarization and the $\mathrm{\Lambda }\to p{\pi }^{-}$ decay asymmetry parameters, and obtain ${\mathcal{A}}_{\mathrm{C}\mathrm{P}}^{\mathrm{p}\mathrm{o}\mathrm{l}}=0.15\pm {0.12}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{.}}\pm {0.04}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{.}}$. We also perform an updated measurement of the absolute branching fraction, resulted as $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }X)=(38.07\pm {0.38}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{.}}\pm {0.49}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{.}})\mathrm{\%}$, with precision improved by a factor of four relative to the current world average. A search for direct CP violation yields ${\mathcal{A}}_{\mathrm{C}\mathrm{P}}^{\mathrm{d}\mathrm{i}\mathrm{r}}=(1.5\pm {1.0}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{.}}\pm {1.0}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{.}})\mathrm{\%}$. No evidence for CP violation in inclusive charm baryon decays is observed.