Coherence Effects in Charmonium Production off Nuclei : Consequences for J/ψSuppression

Abstract

The probabilistic Glauber formula for nuclear absorption used in the literature is only valid at low energies and $x_{+}\simeq 0$. Due to energy conservation, ${\sigma }_{abs}$ is replaced by an effective cross-section ${\sigma }_{abs}+x_{+}^{\gamma }$ (${\sigma }_{c\bar{c}-N}-{\sigma }_{abs})$ which increases with $x_{+}$ and tends to the total $c\bar{c}-N$ cross-section ${\sigma }_{c\bar{c}-N}$. Experimental data can be described with ${\sigma }_{abs}\sim 4÷5$mb and ${\sigma }_{c\bar{c}-N}\sim 15÷20$mb. At high energies, due to the increase of the coherence length, this formula changes. The main change is the replacement of ${\sigma }_{abs}$ by ${\sigma }_{c\bar{c}-N}$ -- for all values of $x_{+}$, as $s\to \infty$. Thus, if ${\sigma }_{c\bar{c}-N}>{\sigma }_{abs}$ the $J/\psi$ suppression due to nuclear interaction will increase with energy.

Talk presented at the International Workshop on Charm Production, ECT*, Trento, June 2002