Interplay of Interference Effects in Production of $J/Ψ$ and $Ψ'$ off Nuclei
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Our main observations are: (i) The effective path length of the $c\bar c$ wave packet, which is produced in the nucleus, grows with the energy of the produced charmonium. The variation is controlled by the coherence length $l_c=2E_Ψ/M^2_Ψ$. (ii) A colorless $c\bar c$ wave packet produced in $pp$-interaction is a specific linear combination of the $J/Ψ$ and $Ψ'$ states, and interacts substantially weaker that any of its components. The time evolution of this wave packet is controlled by the formation length, $l_f=2E_Ψ/(M^2_{Ψ'} - M^2_Ψ)$. Exact formulas incorporating with these effects are derived. The interplay of the two phenomena results in a nontrivial energy- and $x_F$-dependence of the nuclear suppression of the charmonium production in proton-nucleus and nucleus-nucleus collisions and explains some of the experimentally observed effects.
Latex 7 pages, 4 postscript files with figures. Invited talks presented by B. Kopeliovich at the XXXI st Rencontres de Moriond, ''QCD and High-Energy Hadronic Interactions'' March 23-30, 1996, Les Arcs, France and at PANIC'96, May 22-28, 1996, Williamsburg, USA Misprints in eqs. (13) and (14) are corrected
Latex 7 pages, 4 postscript files with figures. Invited talks presented by B. Kopeliovich at the XXXI st Rencontres de Moriond, ''QCD and High-Energy Hadronic Interactions'' March 23-30, 1996, Les Arcs, France and at PANIC'96, May 22-28, 1996, Williamsburg, USA Misprints in eqs. (13) and (14) are corrected