Σ + and Σ ¯ − Polarization in the J / ψ and ψ ( 3686 ) Decays

Le résumé fourni par la source

From $1310.6\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }J/\ensuremath{\psi}$ and $448.1\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\ensuremath{\psi}(3686)$ events collected with the BESIII experiment, we report the first observation of ${\mathrm{\ensuremath{\Sigma}}}^{+}$ and ${\overline{\mathrm{\ensuremath{\Sigma}}}}^{\ensuremath{-}}$ spin polarization in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}J/\ensuremath{\psi}[\ensuremath{\psi}(3686)]\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Sigma}}}^{+}{\overline{\mathrm{\ensuremath{\Sigma}}}}^{\ensuremath{-}}$ decays. The relative phases of the form factors $\mathrm{\ensuremath{\Delta}}\mathrm{\ensuremath{\Phi}}$ have been measured to be $(\ensuremath{-}15.5\ifmmode\pm\else\textpm\fi{}0.7\ifmmode\pm\else\textpm\fi{}0.5)\ifmmode^\circ\else\textdegree\fi{}$ and $(21.7\ifmmode\pm\else\textpm\fi{}4.0\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode^\circ\else\textdegree\fi{}$ with $J/\ensuremath{\psi}$ and $\ensuremath{\psi}(3686)$ data, respectively. The nonzero value of $\mathrm{\ensuremath{\Delta}}\mathrm{\ensuremath{\Phi}}$ allows for a direct and simultaneous measurement of the decay asymmetry parameters of ${\mathrm{\ensuremath{\Sigma}}}^{+}\ensuremath{\rightarrow}p{\ensuremath{\pi}}^{0}({\ensuremath{\alpha}}_{0}=\ensuremath{-}0.998\ifmmode\pm\else\textpm\fi{}0.037\ifmmode\pm\else\textpm\fi{}0.009)$ and ${\overline{\mathrm{\ensuremath{\Sigma}}}}^{\ensuremath{-}}\ensuremath{\rightarrow}\overline{p}{\ensuremath{\pi}}^{0}({\overline{\ensuremath{\alpha}}}_{0}=0.990\ifmmode\pm\else\textpm\fi{}0.037\ifmmode\pm\else\textpm\fi{}0.011)$, the latter value being determined for the first time. The average decay asymmetry, $({\ensuremath{\alpha}}_{0}\ensuremath{-}{\overline{\ensuremath{\alpha}}}_{0})/2$, is calculated to be $\ensuremath{-}0.994\ifmmode\pm\else\textpm\fi{}0.004\ifmmode\pm\else\textpm\fi{}0.002$. The $CP$ asymmetry ${A}_{CP,\mathrm{\ensuremath{\Sigma}}}=({\ensuremath{\alpha}}_{0}+{\overline{\ensuremath{\alpha}}}_{0})/({\ensuremath{\alpha}}_{0}\ensuremath{-}{\overline{\ensuremath{\alpha}}}_{0})=\ensuremath{-}0.004\ifmmode\pm\else\textpm\fi{}0.037\ifmmode\pm\else\textpm\fi{}0.010$ is extracted for the first time, and is found to be consistent with $CP$ conservation.

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