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

V. Guzey, M. Rinaldi, S. Scopetta, M. Strikman, M. Viviani

Published 2022-02-24Version 1

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 (EIC). Using an accurate treatment of the wave functions of $^4$He and $^3$He, we show that this process has the power to disentangle the contributions of the interaction with a specific number of nucleons, in particular, the contribution of two nucleons at the momentum transfer $t \neq 0$. This challenging, first ever calculation of coherent vector meson production on light nuclei, using realistic nuclear wave functions, provides an additional test of models of nuclear shadowing and a novel probe of the gluon distribution in impact parameter representation, allowing for a 3D imaging of gluons in light nuclei. Besides, thanks to this analysis, unique information on the real part of the corresponding scattering amplitude could be accessed.