Accessing directly the strange quark content of the proton at HERA

We investigate a double-spin asymmetry for the semi-inclusive Λ hyperon production in the longitudinally deep inelastic lepton-proton scattering, the sign of which can provide us with important information about the strange quark helicity distribution in the proton. On the basis of the interpretation of the longitudinal deep inelastic lepton-nucleon scattering data as a negative strange quark polarization in the proton and the preliminary results on the measurement of the longitudinal Λ polarization at the Z resonance in electron-positron annihilation, we predict a minus sign for the suggested observable. The experimental condition required for our suggestion is met by the HERA facilities, so the asymmetry considered can be measured by the HERMES experiments at HERA in the near future.