Measurement of ΔS in the nucleon at HERMES from semi-inclusive DIS

The helicity density of the strange quark sea in the proton has been extracted from measurements of polarized semi-inclusive production of charged kaons in deep-inelastic scattering of positrons from a polarized deuteron target. In the region of measurement of x > 0.02 the helicity density is zero within experimental error and the measured first moment of the density is 0.006±0.029(stat.)±0.007(sys.). The first moment of the axial charge in the measured region is substantially less than that inferred from hyperon semi-leptonic decays