New R Values in 2-5 Gev from the Beijing Spectrometer

Abstract

The values of $R = \sigma(e^+e^-\to {hadrons})/\sigma(e^+e^-\to\mu^+\mu^-)$ for 85 center-of-mass energies between 2 and 5 GeV were measured with the upgraded Beijing Spectrometer at the Beijing Electron-Positron Collider, with an average uncertainty of $\sim7%$.