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The spin structure functions of the proton and the deuteron were measured during the EG4 experiment at Jefferson Lab in 2006. Data were collected for longitudinally polarized electron scattering off longitudinally polarized NH3 and ND3 targets, for Q2 values as small as 0.012 and 0.02 GeV2, respectively, using the CEBAF Large Acceptance Spectrometer. This is the archival paper of the EG4 experiment that summarizes the previously reported results of the polarized structure functions g1, A1F1, and their moments 1, γ0, and ITT, for both the proton and the deuteron. In addition, we report on new results on the neutron g1 extracted by combining proton and deuteron data and correcting for Fermi smearing, and on the neutron moments 1, γ0, and ITT formed directly from those of the proton and the deuteron. Our data are in good agreement with the Gerasimov-Drell-Hearn sum rule for the proton, deuteron, and neutron. Furthermore, the isovector combination was formed for g1 and the Bjorken integral p−n 1 ,andit was compared to available theoretical predictions. All of our results, to the best of our knowledge, provide for the first time extensive tests of spin observable predictions from chiral effective field theory (χEFT) in a Q2 range commensurate with the pion mass. They motivate further improvement in χEFT calculations from other approaches such as the lattice gauge method. 

The ratio of the electric to magnetic form factors of the proton, μpGEp/GMp, has been measured for elastic electron-proton scattering with polarized beam and target up to four-momentum transfer squared Q2=5.66(GeV/c)2 using double spin asymmetry for target spin orientation aligned nearly perpendicular to the beam momentum direction. This measurement of μpGEp/GMp agrees with the Q2 dependence of previous recoil polarization data and reconfirms the discrepancy at high Q2 between the Rosenbluth and the polarization-transfer method with a different measurement technique and systematic uncertainties uncorrelated to those of the recoil-polarization measurements. The form factor ratio at Q2=2.06(GeV/c)2 has been measured as μpGEp/GMp=0.720±0.176stat±0.039sys, which is in agreement with an earlier measurement using the polarized target technique at similar kinematics. The form factor ratio at Q2=5.66(GeV/c)2 has been determined as μpGEp/GMp=0.244±0.353stat±0.013sys, which represents the highest Q2 measurement reached using double spin asymmetries with polarized target to date.