First Measurement of the Branching Ratio of $J/\psi\to\gamma f_{2}(1270) f_{2}(1270)$

Abstract

Using 58 million $J/\psi$ events taken with the BES II detector at the Beijing Electron Positron Collider, a new decay mode $J/\psi\to\gamma f_{2}(1270) f_{2}(1270) \to \gamma \pi^+\pi^-\pi^+\pi^-$ is observed for the first time. The branching ratio is determined to be $Br(J/\psi\to\gamma f_{2}(1270) f_{2}(1270))=(9.5\pm0.7\pm1.6)\times 10^{-4}$, where the quoted errors are statistical and systematic, respectively.