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Results and Questions From 4 GeV Running

Jefferson Lab at 4 GeV offered significant improvements over previous experiments. The solid angle of the HMS as well as its large momentum acceptance allowed measurements in previously unexplored regions of $x$ and $Q^2$. A program of measurements with 4 GeV beam ran in Hall C in Summer 1996, and greatly increased the $x$ range of the available data for $1 < Q^2 < 6$ (GeV/c)$^2$. Cross sections were measured at seven angles and are shown in Fig. 4 for the Fe data. Data was also taken on $^2$H, C, and Au targets. Scattered electrons were detected in the HMS and SOS spectrometers using their standard detector packages.

Figure 4: Differential cross section for Fe vs energy loss, $\nu$. The $Q^2$ values given at each angle correspond to Bjorken $x=1$. Statistical errors only are shown.

Cross section were measured for all targets, and a $y$-scaling analysis performed. An article was published in Physical Review Letters [29] describing the inclusive scattering measurement and the analysis of in terms of the $y$-scaling variable. The nuclear structure function was also extracted and scaling in both Bjorken $x$ and Nachtmann $\xi$ have been studied. Also the $Q^2$-dependence of the structure function for fixed bins of $x$ and $\xi$ has been studied. An article was published in Physical Review C [4] presenting the structure function results. These results along with some new results will be summarized in the following sections.

While this experiment was a significant improvement over previous measurements, it was approved for just 8 days of beam time. The emphasis of the measurement was to maximize the $x$ and $Q^2$ coverage on one target (Fe). Lower precision data was taken on the other nuclei. Because of this, there was not enough deuterium data at the highest $x$ and $Q^2$ values to make precise comparisons between the high-$x$ cross sections in heavy nuclei, where multi-nucleon short range correlations are believed to dominate the scattering, and the cross sections from deuterium, where the high-$x$ components are generated entirely by two nucleon short range correlations.