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Strong and Weak $CP$ Tests in Sequential Decays of Polarized ${\Sigma }^{0}$ Hyperons

2024    CERN İşbirliği

The $J/\psi $, $\psi \left(3686\right)\to {\Sigma }^{0}{\overline{\Sigma }}^{0}$ processes and subsequent decays are studied using the world's largest $J/\psi $ and $\psi \left(3686\right)$ data samples collected with the BESIII detector. The parity-violating decay parameters of the decays ${\Sigma }^{0}\to \Lambda \gamma $ and ${\overline{\Sigma }}^{0}\to \overline{\Lambda }\gamma $, ${\alpha }_{{\Sigma }^{0}}=-0.0017±0.0021±0.0018$ and ${\overline{\alpha }}_{{\Sigma }^{0}}=0.0021±0.0020±0.0022$, are measured for the first time. The strong $CP$ symmetry is tested in the decays of the ${\Sigma }^{0}$ hyperons for the first time by measuring the asymmetry ${A}_{CP}^{\Sigma }={\alpha }_{{\Sigma }^{0}}+{\overline{\alpha }}_{{\Sigma }^{0}}=\left(0.4±2.9±1.3\right)×{10}^{-3}$. The weak $CP$ test is performed in the subsequent decays of their daughter particles $\Lambda $ and $\overline{\Lambda }$. Also for the first time, the transverse polarizations of the ${\Sigma }^{0}$ hyperons in $J/\psi $ and $\psi \left(3686\right)$ decays are observed with opposite directions, and the ratios between the $S$-wave and $D$-wave contributions of the $J/\psi $, $\psi \left(3686\right)\to {\Sigma }^{0}{\overline{\Sigma }}^{0}$ decays are obtained. These results are crucial to understand the decay dynamics of the charmonium states and the production mechanism of the ${\Sigma }^{0}-{\overline{\Sigma }}^{0}$ pairs.