The branching ratio of $\Upsilon \mathrm{}\left(3S\right)\mathrm{}\to {\pi }^{+}{\pi }^{-}\Upsilon \mathrm{}\left(1S\right)\mathrm{}$ has been measured to be (4.9 ± 0.9 ± 0.5)%. The di-pion invariant-mass distribution for this decay is flatter than that for the decays $\Upsilon \mathrm{}\left(2S\right)\mathrm{}\to {\pi }^{+}{\pi }^{-}\Upsilon \mathrm{}\left(1S\right)\mathrm{}$ and ${\psi }^{\prime }\to {\pi }^{+}{\pi }^{-}\psi$.

• Received 18 June 1982

DOI:https://doi.org/10.1103/PhysRevLett.49.617