Is J / ψ - Nucleon Scattering Dominated by the

The gluon-exchange contribution to J/ψ-nucleon scattering is shown to yield a sizeable scattering length of about -0.25 fm, which is consistent with the sparse available data. Hadronic corrections to gluon exchange which are generated by ρπ and DD intermediate states of the J/ψ are shown to be negligible. We also propose a new method to study J/ψ-nucleon elastic scattering in the reaction π+d→ J/ψ p p. Submitted to Physics Letters B. Work supported in part by the Department of Energy, contract DE–AC03–76SF00515. Permanent address: Department of Physics, Box 351560, University of Washington, Seattle, Washington 98195-1560 One of the novel features that quantum chromodynamics brings to strong interaction physics is the concept of a gluonic van der Waals potential, the interaction arising from the exchange of two or more gluons between color-singlet hadrons. The color van der Waals potential is expected to be the dominant potential in the case of the scattering of hadrons without common quarks, such as in the interaction of heavy quarkonium states with hadrons or nuclei at low energies. As in quantum electrodynamics, the QCD van der Waals is attractive, and in principle it could lead to molecular-like bound states of charmonium with nuclei[1, 2]. Unlike QED, the QCD van der Waals potential has finite range, rather than the power-law fall-off characteristic of the exchange of massless neutral gauge fields.[3] It is clearly very interesting to study the theoretical foundations and the empirical consequences of the van der Waals potential. In an illuminating paper, Luke, Manohar, Savage[4] have shown that the essential features of the low energy interaction between heavy quarkonium and nucleons or nuclei can be determined directly from the operator product expansion. In their analysis the coupling of multiple gluons to a small-size quarkonium bound state is given by the quarkonium color electric polarizability. The coupling of the gluons to the large-size nucleon or nucleus depends on one term proportional to the momentum fraction carried by gluons and a second term normalized to the nucleon or nuclear mass. The dominant low energy interaction at small relative velocity corresponds to scalar exchange. The gluon exchange potential can then lead to resonances or even bound states in quarkonium-hadron or quarkonium-nuclear interactions. Such novel states could be seen for example as kinematical peaks in the decay of the B meson in the pΛJ/ψ final state.[5] The main purpose of this letter is to demonstrate explicitly that the QCD van der Waals potential as characterized by its scattering length is indeed much more important than the meson-exchange forces in J/ψ-nucleon interactions which arise from the coupling of charmonium to hadronic intermediate states. We also point out that the QCD van der Waals interaction can be conveniently studied experimentally in the highly-constrained reaction πd → J/ψpp. Indirect information on the interactions of the cc system with nucleons can also be obtained from studies of charm production at threshold or, via unitarity, the behavior of pp elastic scattering in the charm threshold region. Indeed the strong increase of the polarization asymmetry ANN observed in Ref. [6] in large CM angle proton-proton 2 scattering at √ s ≃ 5 GeV has been attributed to the strong interactions between charm anti-charm configurations arising in the intermediate state interacting with nucleons at low relative velocity[7]. It would clearly be very useful to verify these physical features from direct measurements of the J/ψ-nucleon interaction. We begin by deriving the scattering length for the QCD van der Waals potential, starting with the Luke, Manohar, Savage LMS two-gluon exchange calculation of the forward invariant amplitude in first Born approximation: Mfwd = 4Mψ M cE ΛQ [ 3 4 V2(ΛQ) + 2π βQαs(ΛQ) ]