MEASUREMENT OF KINEMATIC AND NUCLEAR-DEPENDENCE OF R=SIGMA-L/SIGMA-T IN DEEP-INELASTIC ELECTRON-SCATTERING

We report results on a precision measurement of the ratio R = sigma(L)/sigma(T) in deep inelastic electron-nucleon scattering in the kinematic range 0.2 less-than-or-equal-to x less-than-or-equal-to 0.5 and 1 less-than-or-equal-to Q2 less-than-or-equal-to 10 (GeV/c)2. Our results show, for the first time, a clear falloff of R with increasing Q2. Our R results are in agreement with QCD predictions only when corrections for target mass effects and some additional higher twist effects are included. At small x, the data on R favor structure functions with a large gluon contribution. We also report results on the differences R(A) - R(D) and the cross section ratio sigma(A)/sigma(D) between Fe and Au nuclei and the deuteron. Our results for R(A) - R(D) are consistent with zero for all x, Q2 indicating that possible contributions to R from nuclear higher twist effects and spin-0 constituents in nuclei are not different from those in nucleons. The ratios sigma(A)/sigma(D) from all recent experiments, at all x, Q2 values, are now in agreement.