$J/\psi$-Nucleon Scattering Length and In-medium Mass Shift of $J/\psi$ in QCD Sum Rule Analysis

Abstract

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 ($\rho ,\omega ,\varphi$)-$N$ 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.

Comments: 14 pages, latex, 2 figures included, uses epsf.sty