CoherentJ=?Electroproduction on4Heand3Heat the Electron-Ion Collider:Probing Nuclear Shadowing One Nucleon at a Time br

While the phenomenon of gluon nuclear shadowing at smallxhas been getting confirmation in QCDanalyses of various LHC measurements involving heavy nuclei, it has not been possible so far to establishexperimentally the number of target nucleons responsible for nuclear shadowing in a given process. Toaddress this issue, we study coherentJ=psi electroproduction on4He and3He in the kinematics of a futureelectron-ion collider and show that this process has the power to disentangle the contributions of theinteraction with a specific number of nucleonsk, in particular, with two nucleons at the momentum transfert not equal 0. We predict a dramatic shift of thetdependence of the differential cross section toward smaller valuesofjtjdue to a nontrivial correlation betweenxandk. This calculation, which makes use for the first time ofrealistic wave functions, provides a stringent test of models of nuclear shadowing and a novel probe of the3D imaging of gluons in light nuclei. In addition, thanks to this analysis, unique information on the real partof the corresponding scattering amplitude could be accessed