Measurement of Λ baryon polarization in e+e−→ΛΛ¯ at s=3.773 GeV

Le résumé fourni par la source

Using a data sample of $\ensuremath{\psi}(3770)$ events collected with the BESIII detector at BEPCII corresponding to an integrated luminosity of $2.9\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$, we report a measurement of $\mathrm{\ensuremath{\Lambda}}$ spin polarization in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}\mathrm{\ensuremath{\Lambda}}\overline{\mathrm{\ensuremath{\Lambda}}}$ at $\sqrt{s}=3.773\text{ }\text{ }\mathrm{GeV}$. The significance of polarization is found to be $2\ensuremath{\sigma}$ including the systematic uncertainty, which implies a zero phase between the transition amplitudes of the $\mathrm{\ensuremath{\Lambda}}\overline{\mathrm{\ensuremath{\Lambda}}}$ helicity states. This phase can be interpreted in terms of psionic form factors, and is determined to be $\mathrm{\ensuremath{\Delta}}{\mathrm{\ensuremath{\Phi}}}^{\mathrm{\ensuremath{\Psi}}}={\mathrm{\ensuremath{\Phi}}}_{E}^{\mathrm{\ensuremath{\Psi}}}\ensuremath{-}{\mathrm{\ensuremath{\Phi}}}_{M}^{\mathrm{\ensuremath{\Psi}}}=(7{1}_{\ensuremath{-}46}^{+66}\ifmmode\pm\else\textpm\fi{}5)\ifmmode^\circ\else\textdegree\fi{}$. Similarly, the ratio between the form factors is found to be ${R}^{\ensuremath{\psi}}=|{G}_{E}^{\mathrm{\ensuremath{\Psi}}}/{G}_{M}^{\mathrm{\ensuremath{\Psi}}}|=0.4{8}_{\ensuremath{-}0.35}^{+0.21}\ifmmode\pm\else\textpm\fi{}0.03$. The first uncertainties are statistical and the second systematic.

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