Contribution from Intrinsic Charm Production to Fixed-Target Interactions at the LHC

Abstract

Background: Intrinsic charm, nonperturbative charm in the hadron wavefunction, has long been speculated but has never been satisfactorily proven. Open charm and $J/\psi$ measurements in a fixed-taget configuration at the LHCb searched for this contribution but reported no evidence. Purpose: $\overline D$ meson and $J/\psi$ production is calculated for the SMOG fixed-target configuration in the LHCb experiment using a combination of perturbative QCD and intrinsic charm to see whether intrinsic chaarm would indeed be observable in the SMOG kinematics. Methods: Open charm and $J/\psi$ production is calculated to next-to-leading order in perturbative QCD. Because a gas jet nuclear target is used, cold nuclear matter effects are included in the perturbative calculations. The intrinsic charm is calculated assuming production from a $|uud c \overline c \rangle$ Fock state. Results: The differential rapidity and transverse momentum distributions in $p+{\rm Ne}$, $p+{\rm He}$ and $p+{\rm Ar}$ fixed-target interactions are calculated in the SMOG acceptance and compared to data. The predicted asymmetries between $\overline D$ (leading charm) and $D$ (nonleading charm) are also shown. Conclusions: The contribution from intrinisic charm is small and decreases with center of mass energy. The calculations agree well with the current SMOG data, with or without intrinsic charm.