Spin dependent structure functions with leading-hadron productions

Parton distribution functions in the nucleons have been obtained primarily through lepton-induced deep-inelastic scattering (DIS) experiments. One of the most important unresolved issues in our current knowledge of parton distributions is the role of gluons for describing the nucleon spin. While gluon polarization, ∆G(x), could in principle be deduced from the Q-evolution of the polarized structure functions, g 1(x) and g n 1 (x), measured in the polarized DIS experiments, recent results showed that the gluon polarization is only loosely constrained using this method. The large uncertainty in polarized gluon distribution is reflected in the several very different parametrizations of ∆G(x), all of which can equally well fit the existing data. It is clearly desirable to measure polarized gluon distributions using the strong interaction processes which are sensitive to gluon structure functions at the leading order.