Energy dependence of intrinsic charm production: Determining the best energy for observation
R. Vogt
Abstract
Background: A nonperturbative charm production contribution, known as intrinsic charm, was predicted in the early 1980s. Recent results have provided new evidence for its existence but further confirmation is needed.Purpose: $J/\ensuremath{\psi}$ and $\overline{D}$ meson production are calculated with a combination of perturbative QCD and intrinsic charm to determine the best energy range to study intrinsic charm production.Methods: $J/\ensuremath{\psi}$ and $\overline{D}$ meson production are calculated in perturbative QCD to next-to-leading order in the cross section. Cold nuclear matter effects, including nuclear modification of the parton densities and ${p}_{T}$ broadening by multiple scattering, are taken into account in the production of both; absorption by nucleons is also included for the $J/\ensuremath{\psi}$. Contributions from intrinsic charm are calculated assuming production from a $|uudc\overline{c}\ensuremath{\rangle}$ Fock state.Results: The $J/\ensuremath{\psi}$ and $\overline{D}$ meson rapidity and ${p}_{T}$ distributions are calculated as a function of rapidity and transverse momentum ${p}_{T}$ over a wide range of center-of-mass energies with and without intrinsic charm in $p+p$ collisions. The nuclear modification factor, ${R}_{pA}$, is also calculated for $p+\mathrm{Pb}$ interactions at appropriate energies. Previous fixed-target data as a function of Feynman $x$, ${x}_{F}$, are also compared to calculations within the approach. Good agreement with the data is found when intrinsic charm is included.Conclusions: The intrinsic charm signal may be largest at midrapidity for future low energy fixed target experiments such as the proposed $\mathrm{NA}60+$.