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

Understand

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 $\Upsilon$.