Polarized gluon distribution function of nucleon in diffractive lepto-production of charmonium

Abstract

We investigate the longitudinal double spin asymmetry in the diffractive lepto-production of charmonium off the proton, and study its relation to the polarized gluon distribution Δ G of the proton. It is found that the transverse momenta of the exchanged gluons and Fermi motion of charm quarks give a finite spin asymmetry. Our calculation for the photo-production indicates the asymmetry is small and of O(10 −3) ∼ O(10 −2) at HERA collider energy. On the other hand, at fixed-target energy (HERMES), the asymmetry is of O(10 −2) for J/ψ production. The asymmetry for the ψ′ is even large, of O(10 −1), due to the large Fermi motion of c c in ψ′.