Test of $CP$ Symmetry in the Neutral Decays of $\hat{I}›$ via $J/\ddot{I}ˆ\to \hat{I}›\bar{\hat{I}}›$

Abstract

Using $(10087\pm 44)\times 10^6$ $J/\ddot{I}ˆ$ events collected with the BESIII detector, a full angular distribution analysis is carried out on the process $J/\ddot{I}ˆ\to \hat{I}›\bar{\hat{I}}›\to n\ddot{I}{€}^0\bar{p}\ddot{I}{€}^{+}+c.c.$ The decay parameters $\hat{I}{\pm }_0$ for $\hat{I}›\to n\ddot{I}{€}^0$ and $\bar{\hat{I}}{\pm }_0$ for $\bar{\hat{I}}›\to \bar{n}\ddot{I}{€}^0$ are measured to be $0.668\pm 0.007\pm 0.002$ and $-0.677\pm 0.007\pm 0.003$, respectively, yielding the most precise test for $CP$ symmetry of neutral decays of $\hat{I}›$, $A_{CP}^0=(\hat{I}{\pm }_0+\bar{\hat{I}}{\pm }_0)/(\hat{I}{\pm }_0-\bar{\hat{I}}{\pm }_0)$, to be $-0.006\pm 0.007\pm 0.002$. The ratios $\hat{I}{\pm }_0/\hat{I}{\pm }_{-}$ and $\bar{\hat{I}}{\pm }_0/\hat{I}{\pm }_{+}$ are determined to be $0.884\pm 0.013\pm 0.006$ and $0.885\pm 0.013\pm 0.004$, where $\hat{I}{\pm }_{-}$ and $\hat{I}{\pm }_{+}$ are the decay parameters of $\hat{I}›\to p\ddot{I}{€}^{-}$ and $\bar{\hat{I}}›\to \bar{p}\ddot{I}{€}^{+}$, respectively. The ratios, found to be smaller than unity by more than $5\ddot{I}ƒ$, confirm the presence of the $\hat{I}”I=3/2$ transition in the $\hat{I}›$ and $\bar{\hat{I}}›$ decays, which is expected to improve the theoretical calculations for strong and weak phases, and $A_{CP}$, in hyperon decays. In all results, the first and second uncertainties are statistical and systematic, respectively.

10 pages, 3 figures, 2 tables