Recent Results on the Helicity Structure of the Nucleon from Hermes

The HERMES experiment has measured double spin asymmetries of inclusive and semi-inclusive cross sections for the production of charged hadrons in deep- inelastic scattering of polarised positrons on polarised hydrogen and deuterium targets, in the kinematic range 0.023 < x < 0.6, and 1 GeV² < Q² < 15 GeV². For the data taken on the deuterium target, a RICH detector provides the complete identification of charged pions and kaons. From the inclusive measurements on deuterium, the polarised structure function g_1^d has been extracted with high precision. Together with the semi-inclusive measurements, quark polarisations are extracted separately for the u, ū, d, bar d , and ( s + bar s ) flavours in a LO QCD analysis. Furthermore, a possible breaking of flavour symmetry in the polarised light sea, Δ bar u - Δ bar d , was measured for the first time and found to be consistent with zero within the experimental precision.