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Background: A nonperturbative charm production contribution, known asintrinsic charm, was predicted in the early 1980s. Recent results have providednew evidence for its existence but further confirmation is needed. Purpose:$J/\psi$ and $\bar D$ meson production are calculated with a combination ofperturbative QCD and intrinsic charm to determine the best energy range tostudy intrinsic charm production. Methods: $J/\psi$ and $\bar D$ mesonproduction are calculated in perturbative QCD to next-to-leading order in thecross section. Cold nuclear matter effects, including nuclear modification ofthe parton densities and $p_T$ broadening by multiple scattering are taken intoaccount in the production of both; absorption by nucleons is also included forthe $J/\psi$. Contributions from intrinsic charm are calculated assumingproduction from a $|uud c \bar c \rangle$ Fock state. Results: The $J/\psi$ and$\bar D$ meson rapidity and $p_T$ distributions are calculated as a function ofrapidity and transverse momentum $p_T$ over a wide range of center-of-massenergies with and without intrinsic charm in $p+p$ collisions. The nuclearmodification factor, $R_{pA}$, is also calculated for $p+{\rm Pb}$ interactionsat appropriate energies. Previous fixed-target data as a function of Feynman$x$, $x_F$, are also compared to calculations within the approach. Goodagreement with the data is found when intrinsic charm is included. Conclusions:The intrinsic charm signal may be largest at midrapidity for future low energyfixed target experiments such as the proposed NA60+.

Energy Dependence of Intrinsic Charm Production: What is the Best Energy for Observation?