Nuclear Effects on Charmonium Production

Abstract

$J/\psi$ and ${\psi }^{\prime }$ production cross sections in fixed-target experiment is calculated, considering the contributions from both color-singlet and color-octet mechanisms.The results are applied to the investigations of the $J/\psi$ suppression and the ${\psi }^{\prime }/\psi$ ratio problems in p-A collisions. The results agree with the experimental data as the $(c\bar{c})-$nucleon absorption cross sections ${\sigma }_{abs}^8\simeq 10mb$ for $(c\bar{c}{)}_8$ and ${\sigma }_{abs}^1\simeq 0mb$ for $(c\bar{c}{)}_1$. The model is further used to investigate A-A collisions when comover absorption mechanism is also considered. It is found that the observed experiment data of $J/\psi$ and ${\psi }^{\prime }/\psi$ ratio in S-U collisions and Pb-Pb collisions can not be explained consistently within this model. The possibility of QGP formation in S-U and Pb-Pb collisions is also discussed.

Revtex, 17 pages, 7 figures