Nuclear Effects on Charmonium Production

Abstract

$J/ψ$ and $ψ'$ 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 $J/ψ$ suppression and the $ψ'/ψ$ ratio problems in p-A collisions. The results agree with the experimental data as the $(c \bar c)-$nucleon absorption cross sections $σ_{abs}^8\simeq 10mb $ for $(c \bar c)_8$ and $σ_{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 $J/ψ$ and $ψ'/ψ$ 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.