Measurement of the branching ratio for decay ofΥstates toμ+μ−

Using the Columbia University–Stony Brook detector at the Cornell Electron Storage Ring, we have measured $B_{\mu \mu }$, the branching fraction into muons, of the 1S, 2S, and 3S Υ mesons. We obtain ${\mathit{B}}_{\mathrm{\mu }\mathrm{\mu }}$(1S)=(2.61±0.09±0.11)%, ${\mathrm{\Gamma }}_{\mathrm{tot}}$(1S)=51.1±3.2 keV, ${\mathit{B}}_{\mathrm{\mu }\mathrm{\mu }}$(2S)=(1.38±0.25±0.15)%, ${\mathrm{\Gamma }}_{\mathrm{tot}}$(2S)=42.3±9.2 keV, ${\mathit{B}}_{\mathrm{\mu }\mathrm{\mu }}$(3S)=(1.73±0.15±0.11)%, and ${\Gamma }_{\mathrm{tot}\left(3\mathrm{}\mathrm{S}\right)=27.7\mathrm{}\pm 3.7}$ kev. We also derive, from these results, ${\alpha }_s$=0.174 and ${\Lambda }_{\mathrm{MS}\mathrm{¯}=157\mathrm{}}$ MeV, where MS¯ denotes the modified minimal-subtraction scheme.