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

TL;DR

This paper investigates sub-threshold production of heavy quarkonium in gamma-nucleus collisions to test nucleon-nucleon short-range correlations, providing estimates relevant for future experimental measurements.

Contribution

It introduces a novel approach to probe nucleon-nucleon short-range correlations through sub-threshold heavy quarkonium production in gamma-A collisions.

Findings

Cross sections estimated for sub-threshold $J/\psi$ and $\Upsilon$ production.

SRC contributions become dominant at lower photon energies.

Potential for future experimental validation at JLab and Electron-Ion Collider.

Abstract

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.