A precise extraction of R= σL/ σT from a global analysis of the SLAC deep inelastic e-p and e-d scattering cross sections

We report the extraction of R= σ L/ σ T from a global analysis of eight SLAC deep inelastic experiments on e-p and e-d scattering performed between 1970 and 1985. Values of R p, R d, and R d − R p are determined over the entire SLAC kinematic range: 0.1⩽ x⩽0.9 and 0.6⩽ Q 2⩽20.0 (GeV/ c) 2. We find that R p= R d. Measured values of R( x, Q 2) are larger than predictions based on perturbative QCD and on QCD with the inclusion of kinematic target mass terms, indicating that dynamical higher twist effects may be important in the SLAC kinematic range.