Polarized quark distributions extracted from inclusive and semi-inclusive deeply inelastic scattering at HERMES

The helicity structure of the nucleon can be revealed by the determination of the spin dependent structure function g 1(x,Q 2). This has been done by the HERMES experiment with high precision by measuring double spin asymmetries in inclusive deep inelastic scattering of longitudinally polarized positrons on longitudinally polarized protons or deuterons. Furthermore, semi-inclusive asymmetries of hadrons, pions and kaons were extracted and used to perform a five component separation of the helicity distributions of u, $\bar u$, d, $\bar d$ and s quarks in a LO QCD analysis. In general, the results agree well with phenomenological fits to inclusive data. While these fits predict a negative strange quark polarization, the HERMES result suggests a zero or slightly positive value. A possible breaking of the flavor symmetry of the polarized light sea $\Delta \bar u-\Delta \bar d$ was also investigated and found to be consistent with zero within the experimental precision