Nuclear dependence coefficient $α(A,q_T)$ for the Drell-Yan and J/$ψ$ production

Abstract

Define the nuclear dependence coefficient $α(A,q_T)$ in terms of ratio of transverse momentum spectrum in hadron-nucleus and in hadron-nucleon collisions: $\frac{dσ^{hA}}{dq_T^2}/ \frac{dσ^{hN}}{dq_T^2}\equiv A^{α(A,q_T)}$. We argue that in small $q_T$ region, the $α(A,q_T)$ for the Drell-Yan and J/$ψ$ 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 $α(A,q_T)$ is insensitive to the A for normal nuclear targets. For a color deconfined nuclear medium, the $α(A,q_T)$ becomes strongly dependent on the A. We also show that our $α(A,q_T)$ for the Drell-Yan process is naturally linked to perturbatively calculated $α(A,q_T)$ at large $q_T$ without any free parameters, and the $α(A,q_T)$ is consistent with E772 data for all $q_T$.