Precision Measurement of $R=\frac{{\sigma }_L}{{\sigma }_T}$ and $F_2$ in Deep-Inelastic Electron Scattering

We report new results on a precision measurement of the ratio $R=\frac{{\sigma }_L}{{\sigma }_T}$ and the structure function $F_2$ for deep-inelastic electron-nucleon scattering in the kinematic range $0.2\le x\le 0.5$ and $1\le Q^2\le 10$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. Our results show, for the first time, a clear falloff of $R$ with increasing $Q^2$. Our $R$ and $F_2$ results are in good agreement with QCD predictions only when corrections for target-mass effects are included.