Double-polarization asymmetries for inclusive ep scattering were measured at Jefferson Lab using 2.6 and 4.3 GeV longitudinally polarized electrons incident on a longitudinally polarized NH3 target in the CLAS detector. The polarized structure function g1(x,Q2) was extracted throughout the nucleon resonance region and into the deep inelastic regime, for Q2=0.15–1.64 GeV2. The contributions to the first moment Γ1(Q2)=∫g1(x,Q2) dx were determined up to Q2=1.2 GeV2. Using a parametrization for g1 in the unmeasured low x regions, the complete first moment was estimated over this Q2 region. A rapid change in Γ1 is observed for Q2<1 GeV2, with a sign change near Q2=0.3 GeV2, indicating dominant contributions from the resonance region. At Q2=1.2 GeV2 our data are below the perturbative QCD evolved scaling value.
Physical Review Letters
Fatemi, R.; Biselli, Angela; and CLAS Collaboration, "Measurement of the proton spin structure function g1(x;Q2) for Q2 from 0.15-GeV2 to 1.6-GeV2 with CLAS" (2003). Physics Faculty Publications. 28.
R. Fatemi et al. [CLAS Collaboration], "Measurement of the proton spin structure function g1(x;Q2) for Q2 from 0.15-GeV2 to 1.6-GeV2 with CLAS", Phys. Rev. Lett. 91, 222002 (2003) DOI: 10.1103/PhysRevLett.91.222002