Leptonic Decays of Vector Mesons: the Branching Ratio of the Electron-Positron Decay Mode of the Phi Meson

An experiment designed to measure the branching ratio of the phi meson to $e^{+}{e}^{-}$ was performed at DESY by measuring phi production and phi decay to $e^{+}{e}^{-}$ with the same apparatus. The results of this experiment, based on ${10}^4$ $\varphi \to K^{+}{K}^{-}$ events and 41 $\varphi \to e^{+}{e}^{-}$ events on carbon, yield a branching ratio of (2.9±0.8)×${10}^{-4\mathrm{}}$. This result is compared with various theoretical predictions.