Validity of the Color Dipole Approximation for Diffractive Production of Heavy Quarkonium

Abstract

We study the diffractive photo- and leptoproductions of $J/\psi$ and ${\psi }^{\prime }$ on the proton, and examine the validity of the small-size color dipole approximation to the production of radially excited heavy quarkonium. The dipole model predicts a small ratio of ${\psi }^{\prime }$ to $J/\psi$ photoproduction cross sections, which does not agree with experimental data. We show that this discrepancy originates from a large transverse size of ${\psi }^{\prime }$ which makes the convergence of the transverse size expansion questionable, and the calculation without the dipole approximation turns out to be consistent with the data. Productions of ${{\rm Y}}^{\prime }(2S,3S)$ are also discussed, and the dipole approximation is found to be reasonable for the ${\rm Y}$-family.

minor modifications are made, Phys. Rev. D in press

References in corpus (3)

• Charm production at HERA
• The QCD description of diffractive processes
• Psi' to J/Psi Ratio in Diffractive Photoproduction

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