Diffractive rho-meson Leptoproduction on Polarized Nucleon as a Way to Measure the Polarized Gluon Distribution

The amplitude of diffractive $\rho$ (and open quark) leptoproduction on a polarized target is calculated in the leading log approximation of pQCD using the hadron-parton duality hypothesis. The spin-spin asymmetry is expressed in terms of the spin dependent gluon and quark structure functions in the small $x$ region. Therefore the $\gamma^*+p\to \rho +p$ reaction provides a promising tool to study the spin dependent gluon distribution $\Delta G(x,q^2)$.