Observation of the Transitionϒ′→ϒπ+π−→e+e−π+π−

Abstract

In a sample of 10 000 ${\Upsilon }^{\prime }$ decays observed with our nonmagnetic detector at the Cornell Electron Storage Ring, we find 23 events consistent with the decay ${\Upsilon }^{\prime }\to \Upsilon {\pi }^{+}{\pi }^{-}\to e^{+}{e}^{-}{\pi }^{+}{\pi }^{-}$. We derive a branching fraction of 0.20±0.07 for ${\Upsilon }^{\prime }\to \Upsilon {\pi }^{+}{\pi }^{-}$ and estimates of the partial width for this decay. The invariant-mass spectrum of the pion pairs shows a strong preference for large di-pion mass.