Precision CP Symmetry Test and Polarization Analysis in Σ+ Decays

A stringent test of CP symmetry in hyperon decays is performed using 1.0×1010 J/ψ events and 2.7×109 ψ(3686) events collected by the BESIII experiment. The CP asymmetry in the two-body nonleptonic weak decays Σ+→pπ0 and Σ¯−→p¯π0 is determined to be ACP=−0.0118±0.0083(stat)±0.0028(syst), consistent with CP conservation. The average decay parameter ⟨α0⟩=−0.9869±0.0011(stat)±0.0016(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/ψ and ψ(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 Σ decays and establish a benchmark for future precision studies.