Hard exclusive $J/\psi$ leptoproduction on polarized targets

Abstract

We consider the exclusive production of $J/\psi$ mesons in polarized virtual-photon--proton collisions. We derive helicity amplitudes for the dominant subprocess ${\gamma }^{\ast }g\to J/\psi g$ 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 $\Delta g(x,Q^2)$ of the proton.

Latex, 12 pages, 1 ps figure; typos corrected, some points clarified in the text

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• Backward charmonium production in $\pi N$ collisions
• DIS structure functions and the double-spin asymmetry in ${\rho }^0$ electroproduction within a Regge approach
• Spin dependence of diffractive DIS