Tests of CP symmetry in entangled Ξ0- Ξ ¯ 0 pairs

The J/ψ→Ξ0Ξ¯0 process and subsequent decays are investigated using (10087±44)×106 J/ψ events collected at the BESIII experiment. The decay parameters of Ξ0 and Ξ¯0 are simultaneously measured to be αΞ=-0.3750±0.0034±0.0016, α¯Ξ=0.3790±0.0034±0.0021, φΞ=0.0051±0.0096±0.0018 rad, φ¯Ξ=-0.0053±0.0097±0.0019 rad with unprecedented accuracies, where the first and the second uncertainties are statistical and systematic, respectively. The most precise values for CP asymmetry observables of Ξ0 decay are obtained to be ACPΞ=(-5.4±6.5±3.1)×10-3 and ΔφCPΞ=(-0.1±6.9±0.9)×10-3 rad. For the first time, the weak and strong phase differences are determined to be ζP-ζS=(0.0±1.7±0.2)×10-2 rad and δP-δS=(-1.3±1.7±0.4)×10-2 rad, which are the most precise results for any weakly decaying baryon. These results will play important roles in the studies of the CP violations and polarizations for the strange, charmed, and beauty baryons.