Strong and weak $CP$ tests in sequential decays of polarized $\hat{I}{\pounds }^0$ hyperons

Abstract

The $J/\ddot{I}ˆ,\ddot{I}ˆ(3686)\to \hat{I}{\pounds }^0\bar{\hat{I}}{\pounds }^0$ processes and subsequent decays are studied using the world's largest $J/\ddot{I}ˆ$ and $\ddot{I}ˆ(3686)$ data samples collected with the BESIII detector. The strong-$CP$ symmetry is tested in the decays of the $\hat{I}{\pounds }^0$ hyperons for the first time by measuring the decay parameters, $\hat{I}{\pm }_{\hat{I}{\pounds }^0}=-0.0017\pm 0.0021\pm 0.0018$ and $\bar{\hat{I}}{\pm }_{\hat{I}{\pounds }^0}=0.0021\pm 0.0020\pm 0.0022$. The weak-$CP$ test is performed in the subsequent decays of their daughter particles $\hat{I}›$ and $\bar{\hat{I}}›$. Also for the first time, the transverse polarizations of the $\hat{I}{\pounds }^0$ hyperons in $J/\ddot{I}ˆ$ and $\ddot{I}ˆ(3686)$ decays are observed with opposite directions, and the ratios between the S-wave and D-wave contributions of the $J/\ddot{I}ˆ,\ddot{I}ˆ(3686)\to \hat{I}{\pounds }^0\bar{\hat{I}}{\pounds }^0$ decays are obtained. These results are crucial to understand the decay dynamics of the charmonium states and the production mechanism of the $\hat{I}{\pounds }^0-\bar{\hat{I}}{\pounds }^0$ pairs.