Hard exclusive J/ψ leptoproduction on polarized targets

We consider the exclusive production of J/ψ mesons in polarized virtual-photon–proton collisions. We derive helicity amplitudes for the dominant subprocess γ∗g→J/ψ g and show that polarization asymmetries vanish in the case of collinear scattering. Thus, contrary to what has been suggested earlier, this process is not a good probe of the polarized gluon distribution Δg(x,Q2) of the proton.