Detect \Delta G at BNL-RHIC via Double Quarkonium Production
  The double spin asymmetry for exclusive $J/\psi$ pair production in the polarized $p-p$ collisions at RHIC is investigated. Our study shows that the asymmetry in this process is measurable at RHIC-SPIN experiments in the near future, and, hence it can be used to determine the gluon distribution function $\Delta G (x)$ in the polarized nucleon. 
Jiro Kodaira and Cong-Feng Qiao