Coherent $J/ \psi$ electroproduction on $^4$He and $^3$He at the Electron-Ion Collider: probing nuclear shadowing one nucleon at a time

TL;DR

This paper proposes using coherent $J/\psi$ electroproduction at a future electron-ion collider to experimentally determine the number of nucleons involved in nuclear shadowing, providing insights into gluon distributions in light nuclei.

Contribution

It introduces a novel method to disentangle contributions of specific nucleon numbers in nuclear shadowing using realistic wave functions and predicts observable shifts in the $t$-dependence of the cross section.

Findings

Predicted shift of the $t$-dependence toward smaller $|t|$ values.

Demonstrated the potential to distinguish contributions from different nucleon numbers.

Provided a new approach to probe gluon distributions and nuclear shadowing in light nuclei.

Abstract

While the phenomenon of gluon nuclear shadowing at small $x$ has been getting confirmation in QCD analyses of various LHC measurements involving heavy nuclei, it has not been possible so far to establish experimentally the number of target nucleons responsible for nuclear shadowing in a given process. To address this issue, we study coherent $J / \psi$ electroproduction on $^4$He and $^3$He in the kinematics of a future electron-ion collider and show that this process has the power to disentangle the contributions of the interaction with a specific number of nucleons $k$, in particular, with two nucleons at the momentum transfer $t \neq 0$. We predict a dramatic shift of the $t$-dependence of the differential cross section toward smaller values of $|t|$ due to a non-trivial correlation between $x$ and $k$. This calculation, which makes use for the first time of realistic wave functions, provides a stringent test of models of nuclear shadowing and a novel probe of the 3D imaging of gluons in light nuclei. In addition, thanks to this analysis, unique information on the real part of the corresponding scattering amplitude could be accessed.