Nuclear dependence coefficient α(A,qT)\alpha(A,q_T) for the Drell-Yan and J/ψ\psi production

Define the nuclear dependence coefficient $\alpha(A,q_T)$ in terms of ratio of transverse momentum spectrum in hadron-nucleus and in hadron-nucleon collisions: $\frac{d\sigma^{hA}}{dq_T^2}/ \frac{d\sigma^{hN}}{dq_T^2}\equiv A^{\alpha(A,q_T)}$. We argue that in small $q_T$ region, the $\alpha(A,q_T)$ for the Drell-Yan and J/$\psi$ production is given by a universal function:\ $a+b q_T^2$, where parameters a and b are completely determined by either calculable quantities or independently measurable physical observables. We demonstrate that this universal function $\alpha(A,q_T)$ is insensitive to the A for normal nuclear targets. For a color deconfined nuclear medium, the $\alpha(A,q_T)$ becomes strongly dependent on the A. We also show that our $\alpha(A,q_T)$ for the Drell-Yan process is naturally linked to perturbatively calculated $\alpha(A,q_T)$ at large $q_T$ without any free parameters, and the $\alpha(A,q_T)$ is consistent with E772 data for all $q_T$.Comment: latex, 28 pages, 10 figures, updated two figures, and add more discussion

Universality in nuclear dependence coefficient α(qT)\alpha(q_T)

We derive the nuclear dependence coefficient $\alpha(q_T)$ for Drell-Yan and J/$\psi$ production. We show that at small $q_T$, the $\alpha(q_T)$ is given by an universal functional form: $\alpha(q_T)=a+b q_T^2$, and the parameters $a$ and $b$ are completely determined by either perturbatively calculable or independently measurable quantities. This universal functional form $\alpha(q_T)$ is insensitive to the $A$, and is consistent with existing data.Comment: latex, 4 pages, 3 figures, slightly revise