Measurements of neutrino-nucleon and antineutrino-nucleon differential cross sections using the CCFR neutrino detector at Fermilab have been used to extract preliminary values of $R ={ \sigma_L}/{ \sigma_T}$ in the kinematic region $0.01<x<0.6$, and $4<Q^2<300$ GeV$^2$. The new data provide the first measurements of $R$ in the $x<0.1$ region. The $x$ and $Q^2$ dependence of $R$ is compared with a QCD based fit to previous data. The QCD fit, which provides an estimate of $R$ in small $x$ region where $R$ has not been previously measured, is in good agreement with the new CCFR data.
Categories: hep-ex