arXiv subjects
Publications and source records attributed to Wei-Qin Chao.
Using the General Cascade Program(GCP), the production and absorption of $J/ψ$ in p-A and A-A collisions have been studied. Nucleon absorption mechanism and comover absorption mechanism are considered to investigate the $J/ψ$ suppression. The results agree well with experimental data of $J/ψ$ production, except for the data in Pb-Pb collision.
$J/ψ$ 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.
$J/ψ$ production cross section considering the contributions of both color-singlet and color-octet $c\bar c$ channels is calculated. The result is used to study the suppression of $J/ψ$ in nuclear collisions. With absorption cross sections for $(c \bar c)_8$ $σ_{abs}^8\simeq 11mb $ and $(c \bar c)_1$ $σ_{abs}^1\simeq 0mb $ the p-A and A-B data except for Pb-Pb can be explained. Possible explanations of additional suppression in Pb-Pb are discussed.
The definition of thermal relaxation time is extended to chemically non-equilibrated quark-gluon plasma and the chemical non-equilibrated thermal relaxation times for partons are calculated using the non-equilibrium Debye mass as the infrared regulator. The dependence of the thermal relaxation time on the fugacity is given and the influence of the chemical non-equilibration is discussed. We find that there are threshold fugacities $λ_g^*$ and $λ_q^*$ for gluons and quarks. For λ_g < λ_g^* (λ_q < λ_q^*), τ_g^{NEQ}/τ_g^{EQ} (τ_q^{NEQ}/τ_q^{EQ}) decreases strongly with increasing fugacity, while for $λ_g > λ_g^* (λ_q>λ_q^*$), the ratios are almost 1. It is shown that there is also the two-stage equilibration in a chemically non-equilibrated plasma. We also discussed the effect of using the non-equilibrium Deby mass as the infrared cutoff.
We consider the contributions of both color-singlet and octet $c\bar c$ bound states for studying the suppression of $J/ψ$ production in quark gluon plasma (QGP) and have found that the existence of the color-octet $c\bar c$ may cause the $p_T-$distribution of $J/ψ$ a decrease with $p_T$ after a critical value $(p_T)_{max}$, which is quite different from the behavior in Hadronic Matter (HM).
While presently available p-A data observe that the nuclear dependence of $J/ψ$ and $ψ^{\prime}$ production is the same within errors, we show that different nuclear dependence of $J/ψ$ and $ψ^{\prime}$ production in the kinematic region uncovered by the present p-A data can be predicted based on two different nuclear absorption scenarios. It is found that the predicted production ratio $σ(ψ^{\prime})/σ(J/ψ)$ at positive $x_F$ in A-p collisions is mainly determined by nuclear absorption, and hence allows direct experimental test of nuclear absorption scenarios.