Measurements of the Longitudinal to Transverse Cross Section Ratio and Separated Structure Functions on Nucleons and Nuclei

The ratio R of longitudinal (L) to transverse (T) electron scattering off the nucleon is a fundamental quantity that should be measured with the best possible accuracy. Recent data from experiments in Hall C at Jefferson Lab have measured precision inclusive elastic, quasi-elastic, resonance, and deep inelastic cross sections from nucleons and nuclei over the four-momentum transfer range 0.05 $<$ Q$^{2} \quad <$ 5.50 GeV$^ {2}$. This new data has been used to accurately perform over 200 Rosenbluth- type L/T separations. These separations have allowed for the longitudinal component of the electron-nucleon(us) cross section to be extracted, for the first time in many cases, and for the inelastic structure functions F$_{1}$, F$_{2}$, and F$_{L}$ to be obtained. One surprising observation is that R is large at the larger W, low Q values, where it is typically assumed to go to zero. Other physics issues addressed by the new data include: the nuclear dependence of the longitudinal structure function; quark-hadron duality; structure function moment extractions; a search for nuclear pions; improved measurements of F$_{2}$; and modeling the vector contribution to neutrino cross sections.