Observation of the decay Υ(4S)→Υ(1S)π+π−

Le résumé fourni par la source

We study transitions between $\ensuremath{\Upsilon}$ states with the emission of charged pions using $477\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of data collected with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider. The measured product branching fraction $\mathcal{B}(\ensuremath{\Upsilon}(4S)\ensuremath{\rightarrow}\ensuremath{\Upsilon}(1S){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})\ifmmode\times\else\texttimes\fi{}\mathcal{B}(\ensuremath{\Upsilon}(1S)\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})=(4.42\ifmmode\pm\else\textpm\fi{}0.81(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.56(\mathrm{sys}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. When the PDG value for $\mathcal{B}(\ensuremath{\Upsilon}(1S)\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})$ is used, this corresponds to $\mathcal{B}(\ensuremath{\Upsilon}(4S)\ensuremath{\rightarrow}\ensuremath{\Upsilon}(1S){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})=(1.78\ifmmode\pm\else\textpm\fi{}0.33(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.23(\mathrm{sys}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and a partial decay width $\ensuremath{\Gamma}(\ensuremath{\Upsilon}(4S)\ensuremath{\rightarrow}\ensuremath{\Upsilon}(1S){\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}})=(3.65\ifmmode\pm\else\textpm\fi{}0.67(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.65(\mathrm{sys}))\text{ }\text{ }\mathrm{keV}$.

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