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QCD Mechanisms for Double Quarkonium and Open Heavy Meson Hadroproduction

Double $J/ψ$ production on the order of 20-30 pb has been observed by the NA3 collaboration. These $ψψ$ pairs, measured in $π^- N$ interactions at 150 and 280 GeV$/c$ and in $pN$ interactions at 400 GeV$/c$, carry a large fraction of the projectile momentum, $x_{ψψ} \geq 0.6$ for the 150 GeV$/c$ beam and $\geq 0.4$ at 280 GeV$/c$. We examine several sources of $ψψ$ pair production within QCD, including ${\cal O}(α_s^4)$ $ψψ$ production, leading-twist $b \overline b$ production and decay, and the materialization of heavy-quark Fock states in the projectile. We estimate the production cross section and the single and double $J/ψ$ momentum and mass distributions for each, comparing the results with the NA3 data, and predict $ψψ$ production in $pN$ interactions at 800 GeV$/c$, accessible to current fixed-target experiments. We also discuss the observable implications of open heavy meson pair production from the intrinsic heavy quark Fock states.