The $g_{J/\psi D_s D_s}$ strong coupling constant from QCD Sum Rules

The coupling constant of the meson vertex $J/\psi D_s D_s$ is calculated using the three point correlation function within the QCD Sum Rule formalism. We have considered alternately mesons $J/\psi$ and $D_s$ off-shell together with non-perturbative contributions up to the mixed quark-gluon condensates. When extrapolated, these two different form factors give the same coupling constant for the process $g_{J/\psi D_s D_s} = 5.98^{+0.67}_{-0.58}$.