Sub-threshold $J/\psi$ and $\Upsilon$ Production in $\gamma A$ Collisions

We study sub-threshold heavy quarkonium ($J/\psi$ and $\Upsilon$) photo-productions in $\gamma A$ collisions as an independent test of the universality of the nucleon-nucleon short range correlation (SRC) in nuclear scattering processes. Just below the $\gamma p$ threshold, the cross section is dominated by the mean field contribution of nucleons inside the nucleus. The SRC contributions start to dominate at lower photon energies, depending on the fraction of the SRC pairs in the target nucleus. We give an estimate of the cross sections in the sub-threshold region both for $J/\psi$ and $\Upsilon$. This may be helpful for future measurements at JLab as well as at the Electron-Ion Collider in the U.S., and especially in China.