Spin Structure Functions of the Proton and Deuteron from SLAC Experiments E155 and E155X

Experiments E155 and E155X at SLAC were polarized deep inelastic scattering measurements of the parallel and perpendicular scattering asymmetries. We extracted the polarized structure functions g₁ and g₂ of the proton and deuteron. Both experiments made precision measurements through a wide range in x and Q². These data fall into the kinematic range between existing world data and have good consistency with them. In combination with the other world data, the results for g₁ allow increased constraint on NLO QCD fits to the polarized structure functions. For g₂ no significant world data existed before E155X. The E155X measurement provides information about the higher twist effects in the nucleon.