Joint ECFA-NuPECC-APPEC Workshop “Synergies between the EIC and the LHC”

We investigate the exclusive production of the pseudoscalar meson $\eta_c$ in electron-ion collisions through $\gamma^* \gamma$ interactions. At high energies, this process is dominated by photon-photon fusion, enhanced by the strong nuclear photon flux. We present cross-section predictions for future facilities (EIC, EicC, LHeC), focusing on rapidity, transverse momentum, and photon virtuality distributions. The analysis explores different models for the $\eta_c$ wave function, showing how such measurements can constrain the meson's transition form factor and offer new insights into its internal structure.