Double-Spin Asymmetry of J/psi Production in Polarized pp Collisions at   HERA-$\vec N$
  We calculated the color-octet contribution to the double spin asymmetry of $J/\psi$ hadroproduction with nonzero transverse momenta at fixed target energies $\sqrt{s}\simeq40$ GeV. It is shown that the color-octet contribution is dominant in the asymmetries. The expected asymmetries and statistical errors in a future option of HERA with longitudinally polarized protons at HERA-$\vec N$ should allow one to distinguish between different parametrizations for the polarized gluon distribution in the proton. 
Oleg Teryaev and Avto Tkabladze