Compass Measurement of g1 and QCD Fits

We present the latest COMPASS results on the proton spin structure function g1p(x) at 200GeV. The data improve the statistical precision by a factor of ∼2 at low x. A reevaluation of the Bjorken sum rule based on COMPASS proton and deuteron data confirms its validation to a 9% accuracy. Finally, results from a global NLO QCD fit of g1 world data are shown. The extracted spin singlet distribution leads to an integrated value of 0.26 < ΔΣ < 0.34 at Q2 = 3 (GeV/c)2. The large uncertainty is mainly driven by the unknown shape of the distribution.