Color screening and the suppression of the charmonium state yield in nuclear reactions

We discuss the negative Feynman-x regime of the new data for the production of the ψ′ meson in pA collisions at 450 GeV at CERN-SPS (of the NA50 Collaboration). We extract from the CERN data σ(ψ′ N) ≈ 8 mb under the assumption that the ψ′ is produced as a result of the space-time evolution of a pointlike cc̄ pair which expands with time to the full size of the charmonium state. In the analysis we assume the existence of a relationship between the distribution of color in a hadron and the cross section of its interaction with a nucleon. However, our result is rather sensitive to the pattern of the expansion of the wave packet and significantly larger values of σ(ψ′ N) are not ruled out by the data. We show that recent CERN data confirm the suggestion of Gerland et al. [Phys. Rev. Lett. 81, 762 (1998); Nucl. Phys. A663, 1019 (2000)] that color fluctuations of the strengths in charmonium-nucleon interaction are the major source of suppression of the J/ψ yield as observed at CERN in both pA and AA collisions.