The strange quark polarization from COMPASS data

The strange quark helicity distribution $\Delta s(x)$ was derived at LO from the inclusive asymmetry $A_{1,d}$ and the semi-inclusive asymmetries $A^{\pi+}_{1,d}$, $A^{\pi-}_{1,d}$ , $A^{K+}_{1,d}$, $A^{K-}_{1,d}$ measured by COMPASS in polarised deep inelastic muon-deuteron scattering. The distribution of $\Delta s(x)$ is compatible with zero in the whole measured range. The value of the rst moment of $\Delta s$ and its error are very sensitive to the assumed value of the ratio of the $\bar{s}$-quark to $u$-quark fragmentation functions into positive kaons $\int D^{K^{+}}_{\overline{s}}(z)dz/\int D^{K^{+}}_{u}(z)dz$.