Experimental Study of the 3He and Neutron Spin Structures at Low Q2 and the Upgrade of the JLab Polarized 3He Target

In the scattering process off a nuclear or nucleon target, the Gerasimov-Drell-Hearn (GDH) sum rule for real photons ($Q^2$=0 where $Q^2\equiv -q^2$ with $q$ the photon's 4-momentum) relates static properties of the target particle's ground state to dynamic properties of all its excited states. On the other side of the $Q^2$ spectrum, the Bjorken sum rule holds in the Bjorken limit $Q^2 \rightarrow \infty$. Bjorken sum rule relates the final structure functions of the proton and neutron to the nucleon axial coupling constant in weak decay. These two sum rules belong to domains where calculations are achievable but use different degrees of freedom: hadronic degrees of freedom at low $Q^2$ versus partonic degrees of freedom at intermediate $Q^2$. Meanwhile, different methods have been used to connect the two sum rules at finite $Q^2$ values: Chiral Perturbation Theory is used to expand the GDH sum rule while Operator Product Expansion is used to expand the Bjorken sum rule.
In recent decades, improvements in polarized beam and polarized target techniques have made it possible to test theoretical predictions in the intermediate $Q^2$ region. During the Jefferson Lab (JLab) Hall A E97110 experiment, a precise measurement of polarized cross sections was performed at $0.02