Using the CLEO detector at the Cornell Electron Storage Ring, we have measured the muonic branching fractions $B_{\mu \mu }$ of the Υ(1S) and Υ(3S) to be (2.52±0.07±0.07)% and (2.02±0.19±0.33)%, respectively.

• Received 14 February 1989

DOI:https://doi.org/10.1103/PhysRevD.39.3528