Precision $ CP$ Symmetry Test and Polarization Analysis in $ {\mathrm{\Sigma }}^{+}$ Decays

A stringent test of $ CP$ symmetry in hyperon decays is performed using $ 1.0\times {10}^{10}\text{}\text{}J/\psi $ events and $ 2.7\times {10}^{9}\text{}\text{}\psi (3686)$ events collected by the BESIII experiment. The $ CP$ asymmetry in the two-body nonleptonic weak decays $ {\mathrm{\Sigma }}^{+}\to p{\pi }^{0}$ and $ {\overline{\mathrm{\Sigma }}}^{-}\to \overline{p}{\pi }^{0}$ is determined to be $ {A}_{CP}=-0.0118\pm 0.0083(\mathrm{stat})\pm 0.0028(\mathrm{syst})$, consistent with $ CP$ conservation. The average decay parameter $ ⟨{\alpha }_{0}⟩=-0.9869\pm 0.0011(\mathrm{stat})\pm 0.0016(\mathrm{syst})$ represents the most precise measurement in the baryon sector to date. A model-independent analysis of the hyperon polarization is performed for the first time at $ J/\psi $ and $ \psi (3686)$ resonances, revealing a clear sign reversal and offering new insight into SU(3) symmetry breaking and baryon internal structure. These results provide the most stringent constraints on $ CP$ violation in $ \mathrm{\Sigma }$ decays and establish a benchmark for future precision studies.