Interplay of Interference Effects in Production of $J/\Psi$ and ${\Psi }^{\prime }$ off Nuclei

Abstract

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 $l_c=2E_{\Psi }/M_{\Psi }^2$. (ii) A colorless $c\bar{c}$ wave packet produced in $pp$-interaction is a specific linear combination of the $J/\Psi$ and ${\Psi }^{\prime }$ states, and interacts substantially weaker that any of its components. The time evolution of this wave packet is controlled by the formation length, $l_f=2E_{\Psi }/(M_{{\Psi }^{\prime }}^2-M_{\Psi }^2)$. 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.

Comments: 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