Exclusive $J/\psi$ photoproduction and gluon polarization

Abstract

In exclusive $J/\psi$ production by polarized photons incident on polarized protons, a finite polarization asymmetry arises because of $c\bar{c}$ Fermi-motion and binding-energy effects. The asymmetry depends on the polarized nonforward gluon distribution of the proton and thus gives information on gluon polarization in the proton. The analyzing power, however, is rather small.

Comments: 11 pages, Latex, psfig, 2 figures; v2: references and acknowledgement updated; v3: sign of asymmetry reversed, conclusions unchanged, to appear in Phys. Lett. B