Test of CP Symmetry in Hyperon to Neutron Decays

Le résumé fourni par la source

The quantum entangled $J/\ensuremath{\psi}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Sigma}}}^{+}{\overline{\mathrm{\ensuremath{\Sigma}}}}^{\ensuremath{-}}$ pairs from $(1.0087\ifmmode\pm\else\textpm\fi{}0.0044)\ifmmode\times\else\texttimes\fi{}{10}^{10}\text{ }\text{ }J/\ensuremath{\psi}$ events taken by the BESIII detector are used to study the nonleptonic two-body weak decays ${\mathrm{\ensuremath{\Sigma}}}^{+}\ensuremath{\rightarrow}n{\ensuremath{\pi}}^{+}$ and ${\overline{\mathrm{\ensuremath{\Sigma}}}}^{\ensuremath{-}}\ensuremath{\rightarrow}\overline{n}{\ensuremath{\pi}}^{\ensuremath{-}}$. The $CP$-odd weak decay parameters of the decays ${\mathrm{\ensuremath{\Sigma}}}^{+}\ensuremath{\rightarrow}n{\ensuremath{\pi}}^{+}$ (${\ensuremath{\alpha}}_{+}$) and ${\overline{\mathrm{\ensuremath{\Sigma}}}}^{\ensuremath{-}}\ensuremath{\rightarrow}\overline{n}{\ensuremath{\pi}}^{\ensuremath{-}}$ (${\overline{\ensuremath{\alpha}}}_{\ensuremath{-}}$) are determined to be $0.0481\ifmmode\pm\else\textpm\fi{}0.003{1}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.001{9}_{\mathrm{syst}}$ and $\ensuremath{-}0.0565\ifmmode\pm\else\textpm\fi{}0.004{7}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.002{2}_{\mathrm{syst}}$, respectively. The decay parameter ${\overline{\ensuremath{\alpha}}}_{\ensuremath{-}}$ is measured for the first time, and the accuracy of ${\ensuremath{\alpha}}_{+}$ is improved by a factor of 4 compared to the previous results. The simultaneously determined decay parameters allow the first precision $CP$ symmetry test for any hyperon decay with a neutron in the final state with the measurement of ${A}_{CP}=({\ensuremath{\alpha}}_{+}+{\overline{\ensuremath{\alpha}}}_{\ensuremath{-}})/({\ensuremath{\alpha}}_{+}\ensuremath{-}{\overline{\ensuremath{\alpha}}}_{\ensuremath{-}})=\ensuremath{-}0.080\ifmmode\pm\else\textpm\fi{}0.05{2}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.02{8}_{\mathrm{syst}}$. Assuming $CP$ conservation, the average decay parameter is determined as $⟨{\ensuremath{\alpha}}_{+}⟩=({\ensuremath{\alpha}}_{+}\ensuremath{-}{\overline{\ensuremath{\alpha}}}_{\ensuremath{-}})/2=\ensuremath{-}0.0506\ifmmode\pm\else\textpm\fi{}0.002{6}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.001{9}_{\mathrm{syst}}$, while the ratios ${\ensuremath{\alpha}}_{+}/{\ensuremath{\alpha}}_{0}$ and ${\overline{\ensuremath{\alpha}}}_{\ensuremath{-}}/{\overline{\ensuremath{\alpha}}}_{0}$ are $\ensuremath{-}0.0490\ifmmode\pm\else\textpm\fi{}0.003{2}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.002{1}_{\mathrm{syst}}$ and $\ensuremath{-}0.0571\ifmmode\pm\else\textpm\fi{}0.005{3}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.003{2}_{\mathrm{syst}}$, where ${\ensuremath{\alpha}}_{0}$ and ${\overline{\ensuremath{\alpha}}}_{0}$ are the decay parameters of the decays ${\mathrm{\ensuremath{\Sigma}}}^{+}\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{0}$ and ${\overline{\mathrm{\ensuremath{\Sigma}}}}^{\ensuremath{-}}\ensuremath{\rightarrow}\overline{p}{\ensuremath{\pi}}^{0}$, respectively.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.