Longitudinal-Transverse Separations of Deep-Inelastic Structure Functions at Low $Q^2$ for Hydrogen and Deuterium

We report on a study of the longitudinal to transverse cross section ratio, $R={\sigma }_L/{\sigma }_T$, at low values of $x$ and $Q^2$, as determined from inclusive inelastic electron-hydrogen and electron-deuterium scattering data from Jefferson Laboratory Hall C spanning the four-momentum transfer range $0.06<Q^2<2.8{\mathrm{GeV}}^2$. Even at the lowest values of $Q^2$, $R$ remains nearly constant and does not disappear with decreasing $Q^2$, as might be expected. We find a nearly identical behavior for hydrogen and deuterium.

Figure 1

Comparison of the values of $R(x,Q^2)$ for hydrogen from the present experiment (E99-118) to the results of other experiments. The dashed curves represent the parametrization $R_{e99118}^H(x,Q^2)$ and the solid curves the model developed in 15 (see text for details). The dot-dashed curves are a next-to-next-to-leading order calculation based on the recent MRST parton distributions [16], and the dotted curves show the next-to-leading order result of the GRV model [17]. In both cases target mass effects have been included according to 18.

Figure 2

The difference $R^D-R^H$ as a function of $Q^2$ from the present experiment calculated via Rosenbluth separation. The data from previous experiments are also shown for $Q^2<5{\mathrm{GeV}}^2$.