Measurement of the branching ratio for Υ ’ ’ →μμ

Using the CUSB-II detector at the Cornell Electron Storage Ring, we have measured B\ensuremath{\mu}\ensuremath{\mu}, the branching fraction into muons, of the \ensuremath{\Upsilon}'' meson. We find ${\mathit{B}}_{\mathrm{\ensuremath{\mu}}\mathrm{\ensuremath{\mu}}}$(\ensuremath{\Upsilon}'')=(1.53\ifmmode\pm\else\textpm\fi{}0.33\ifmmode\pm\else\textpm\fi{}0.21)%, from which the \ensuremath{\Upsilon}'' total decay width is 25.5\ifmmode\pm\else\textpm\fi{}5.0 keV. From this result we obtain ${\mathrm{\ensuremath{\alpha}}}_{\mathrm{s}}$=0.${170}_{\mathrm{\ensuremath{-}}0.012}^{+0.015}$, ${\ensuremath{\Lambda}}_{\mathrm{MS}\mathrm{\ifmmode\bar\else\textasciimacron\fi{}}{=148}_{\mathrm{\ensuremath{-}}39}^{+56}}$ MeV. (MS\ifmmode\bar\else\textasciimacron\fi{} denotes the modified minimal-subtraction scheme).