Intrinsic Charm Contribution to Double Quarkonium Hadroproduction

Abstract

Double $J/ψ$ production has been observed by the NA3 collaboration in $πN$ and $p N$ collisions with a cross section of the order of 20-30 pb. The $ψψ$ pairs measured in $π^- $ nucleus interactions at 150 and 280 GeV$/c$ are observed to carry an anomalously large fraction of the projectile momentum in the laboratory frame, $x_{ψψ} \geq 0.6$ at 150 GeV$/c$ and $\geq 0.4$ at 280 GeV$/c$. We postulate that these forward $ψψ$ pairs are created by the materialization of Fock states in the projectile containing two pairs of intrinsic $c \overline c$ quarks. We calculate the overlap of the charmonium states with the $|\overline u d c \overline c c \overline c \rangle$ Fock state as described by the intrinsic charm model and find that the $π^- N \rightarrow ψψ$ longitudinal momentum and invariant mass distributions are both well reproduced. We also discuss double $J/ψ$ production in $pN$ interactions and the implications for other heavy quarkonium production channels in QCD.