J/ -Nucleon Scattering Length and In-Medium Mass Shift of J/ in QCD Sum Rule Analysis

We calculate the spin-averaged $J/\psi$-nucleon scattering length$a_{J/\psi}$ by directly applying QCD sum rule to $J/\psi$-$N$ forwardscattering amplitude. Our result $a_{J/\psi} = - 0.10 \pm 0.02$ fm, predictsthe possibility of bound states with nuclei, though the force is weaker thanthat of the light vector mesons ($\rho,\omega,\phi$)-$N$ cases. Up todimension-4 gluonic operators, we evaluate the scattering length with twist-2contribution, which increases the absolute value of the scattering length about30%. If we apply $a_{J/\psi}$ to the effective mass of $J/\psi$ in nuclearmatter on the basis of the linear density approximation, it shows very slightdecrease ($4 \sim 7$ MeV) at normal matter density.Comment: 14 pages, latex, 2 figures included, uses epsf.st