Direct measurement of theJ/ψ leptonic branching fraction

Le résumé fourni par la source

The Mark III Collaboration has measured the J/\ensuremath{\psi} leptonic branching fractions using the process \ensuremath{\psi}(2S)\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{+}$${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$J/\ensuremath{\psi}, J/\ensuremath{\psi}\ensuremath{\rightarrow}${\mathit{l}}^{+}$${\mathit{l}}^{\mathrm{\ensuremath{-}}}$. The results are B(J/\ensuremath{\psi}\ensuremath{\rightarrow}${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$)=(5.92\ifmmode\pm\else\textpm\fi{}0.15\ifmmode\pm\else\textpm\fi{}0.20)% and B(J/\ensuremath{\psi}\ensuremath{\rightarrow}${\mathrm{\ensuremath{\mu}}}^{+}$${\mathrm{\ensuremath{\mu}}}^{\mathrm{\ensuremath{-}}}$)=(5.90\ifmmode\pm\else\textpm\fi{}0.15\ifmmode\pm\else\textpm\fi{}0.19)%, where the first error is statistical and the second is systematic. Assuming lepton universality, the leptonic branching fraction of the J/\ensuremath{\psi} is (5.91\ifmmode\pm\else\textpm\fi{}0.11\ifmmode\pm\else\textpm\fi{}0.20)%. This result is used to obtain the strong coupling constant ${\mathrm{\ensuremath{\alpha}}}_{\mathit{s}}$ and the QCD scale factor ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{MS}}$ (MS\ifmmode\bar\else\textasciimacron\fi{} denotes the modified minimal-subtraction scheme).

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