Stringent test of $CP$ symmetry in $\hat{I}{\pounds }^{+}$ hyperon decays

Abstract

The non-leptonic two-body weak decays $\hat{I}{\pounds }^{+}\to p\ddot{I}{€}^0$ and $\bar{\hat{I}}{\pounds }^{-}\to \bar{p}\ddot{I}{€}^0$ are investigated, utilizing $(1.0087\pm 0.0044)\times 10^{10}$ $J/\ddot{I}ˆ$ events and $(2.7124\pm 0.0143)\times 10^9$ $\ddot{I}ˆ(3686)$ events collected by BESIII experiment. The precision of the weak-decay parameters for the decays $\hat{I}{\pounds }^{+}\to p\ddot{I}{€}^0$ ($\hat{I}{\pm }_0$) and $\bar{\hat{I}}{\pounds }^{-}\to \bar{p}\ddot{I}{€}^0$ ($\bar{\hat{I}}{\pm }_0$) is improved by a factor of three compared to the previous world average. Furthermore, the quantum-entangled $\hat{I}{\pounds }^{+}\bar{\hat{I}}{\pounds }^{-}$ system enables the most precise test of $CP$ symmetry for the decay $\hat{I}{\pounds }^{+}\to p\ddot{I}{€}^0$, through the asymmetry observable $A_{CP}=(\hat{I}{\pm }_0+\bar{\hat{I}}{\pm }_0)/(\hat{I}{\pm }_0-\bar{\hat{I}}{\pm }_0)$ that is measured to be $-0.0118\pm 0.0083_{\mathrm{stat}}\pm 0.0028_{\mathrm{syst}}$. Assuming $CP$ conservation, the average decay parameter is determined to be $⟨\hat{I}{\pm }_0⟩=(\hat{I}{\pm }_0-\bar{\hat{I}}{\pm }_0)/2=-0.9869\pm 0.0011_{\mathrm{stat}}\pm 0.0016_{\mathrm{syst}}$, which is the most precise measurement of the asymmetry decay parameters in baryon sectors. The angular dependence of the ratio of the polarization of the $\hat{I}{\pounds }^{+}$ in both $J/\ddot{I}ˆ$ and $\ddot{I}ˆ(3686)$ decays is studied for the first time.