Improved measurement of $\psi (2S)$ decays into $\tau ^{+}\tau ^{-}$

Abstract

Using 14M $\psi (2S)$ events collected at BESII, the branching fraction of $\psi (2S)\to \tau ^{+}\tau ^{-}$ is measured to be $Br_{\tau \tau}=(3.10\pm 0.21\pm 0.38)\times 10^{-3}$, where the first error is statistical and the second is systematic.