We calculate the spin-averaged $J/\psi$-nucleon scattering length $a_{ J/\psi}$ by directly applying QCD sum rule to $J/\psi$-$N$ forward scattering amplitude. Our result $a_{ J/\psi} = - 0.10 \pm 0.02$ fm, predicts the possibility of bound states with nuclei, though the force is weaker than that of the light vector mesons ($\rho,\omega,\phi$)-$N$ cases. Up to dimension-4 gluonic operators, we evaluate the scattering length with twist-2 contribution, which increases the absolute value of the scattering length about 30%. If we apply $a_{ J/\psi}$ to the effective mass of $J/\psi$ in nuclear matter on the basis of the linear density approximation, it shows very slight decrease ($4 \sim 7$ MeV) at normal matter density.
Categories: nucl-th