Intrinsic Charm Contribution to Double Quarkonium Hadroproduction.pdf

a r X i v : h e p - p h / 9 5 0 3 2 0 6 v 1 2 M a r 1 9 9 5 Intrinsic Charm Contribution to Double Quarkonium Hadroproduction? R. Vogt Nuclear Science Division, Lawrence Berkeley Laboratory, Berkeley, CA 94720, USA and Institute for Nuclear Theory, University of Washington, Seattle, WA 98195, USA S. J. Brodsky Stanford Linear Accelerator Center, Stanford University, Stanford, CA 94309, USA Double J/ψ production has been observed by the NA3 collaboration in πN and pN 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, xψψ ≥ 0.6 at 150 GeV/c and ≥ 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 cc quarks. We calculate the overlap of the charmonium states with the |udcccc〉 Fock state as described by the intrinsic charm model and find that the π?N → 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. ? This work was supported in part by the Director, Office of Energy Research, Division of Nuclear Physics of the Office of High Energy and Nuclear Physics of the U. S. Department of Energy under Contract Numbers DE-AC03-76SF0098 and DE-AC03-76SF00515. 1 Introduction It is quite rare for two charmonium states to be produced in the same hadronic collision. However, the NA3 collaboration has measured a double J/ψ production rate significantly above background in multi-muon events with π? beams at laboratory momentum 150 and 280 GeV/c [1] and a 400 GeV/c proton beam [2]. The integrated π?N → ψψX production cross section, σψψ , is 18 ± 8 pb at 150 GeV/c and 30 ± 10 pb at 280 GeV/c, and the pN → ψψX cross section is 27± 10 pb