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

Abstract

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: $\frac{d{\sigma }^{hA}}{d{q}_T^2}/\frac{d{\sigma }^{hN}}{d{q}_T^2}\equiv A^{\alpha (A,q_T)}$. 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 $q_T$.

Comments: latex, 28 pages, 10 figures, updated two figures, and add more discussions