Spin structure functions: a window into the structure of hadrons

Abstract

A large program of spin structure measurements is underway in Jefferson Lab's Hall B. Of particular interest is the first moment of the spin structure function g1, which goes through a rapid transition from the photon point (Q2 = 0), where it is constrained by the Gerasimov-Drell-Hearn sum rule, to the deep inelastic limit where it is sensitive to the nucleon spin fraction carried by quarks. One can then study the transition from hadronic to quark degrees of freedom over the whole range of Q2. It is also interesting to look for the onset of quark-hadron duality in spin structure functions. We use longitudinally polarized electrons with energies from 1.6 to 5.7 GeV incident upon polarized NH3 and ND3 targets to investigate proton and deuteron spin observables in and above the resonance region. We present the GDH and Bjorken integrals using the 1.6 and 5.7 GeV data and comment on the validity of local quark-hadron duality over the wide kinematical range (0.05 ⩽ Q2 ⩽ 4.5 GeV2 and W < 3.2 GeV) covered by this experiment.