Nucleon off-shell structure and the free neutron valence structure from A=3 inclusive electron scattering measurements

Understanding the differences between the distribution of quarks bound in protons and neutrons is key for constraining the mechanisms of SU(6) spin-flavor symmetry breaking in Quantum Chromodynamics (QCD). The recent MARATHON experiment attempted to extract neutron structure with reduced model dependence by comparing scattering from He-3 and tritium, isospin mirror nuclei.

Here we evaluate the model dependence of this extraction using a convolution framework with available light nuclear DIS data (A < 4), examining the effect of using instant-form and light-cone nuclear wave functions, and several different parameterizations of nucleon modification effects, including those with and without isospin dependence.

We find that inclusive DIS data on light nuclei provide substantial constraints on the neutron-to-proton strucutre function ratio, favoring SU(6) symmetry breaking models based on perturbative QCD and the Schwinger-Dyson equation calculation, though unable to definitively out scalar di-quark models when assuming a wide range of nucleon modification models. We also find that the MARATHON data provides robust constraints on the underlying nucleon modification model, especially when considering isospin dependent effects.