First Measurement of the Isospin-Dependence of Nuclear Structure Functions at 12 GeV JeffersonLab

The structure functions of protons and neutrons provide crucial insight into how the strong nuclear force, as described by Quantum Chromodynamics (QCD), manifests at everyday energies, allowing us to better understand precisely how quarks and gluons interact to form the basic building blocks of almost all visible mass in our universe. Despite more than 40 years of experimental and theoretical effort, the EMC effect -- the observation that nuclear structure functions appear to be modified from those of free nucleons -- is still not fully understood. One open question that remains is whether or not the modification of quark distributions is the same for all quark flavors. Determining the flavor (isospin) dependence of the EMC effect, which is predicted by several models, is essential for coming to a complete understanding of how QCD manifests in nuclei. To this end, inclusive electron Deep Inelastic Scattering (DIS) from nuclei with approximately constant atomic mass number A and variable proton-to-neutron ratio N/Z was measured in Jefferson Lab experiment E12-10-008 to look for isospin-dependent modification of nuclear structure functions. The preliminary EMC ratios presented here cover a kinematic range of 2.8<Q^2<8.1 GeV^2 and 0.18<x_{Bj}<1.0. The size of the EMC effect in these nuclei is extracted by calculating the slope of the EMC ratio as a function of Bjorken x (x_{Bj}) over the ranges 0.3<x_{Bj}<0.6 and 0.3<x_{Bj}<0.7; these slopes then are compared with existing world data. Our preliminary results do not appear to indicate significant isospin-dependence of the EMC effect, though a more careful study is needed once all results are confirmed.